text: #
  # turtle.py: a Tkinter based turtle graphics module for Python
  # Version 1.1b - 4. 5. 2009
  #
  # Copyright (C) 2006 - 2010  Gregor Lingl
  # email: glingl@aon.at
  #
  # This software is provided 'as-is', without any express or implied
  # warranty.  In no event will the authors be held liable for any damages
  # arising from the use of this software.
  #
  # Permission is granted to anyone to use this software for any purpose,
  # including commercial applications, and to alter it and redistribute it
  # freely, subject to the following restrictions:
  #
  # 1. The origin of this software must not be misrepresented; you must not
  #    claim that you wrote the original software. If you use this software
  #    in a product, an acknowledgment in the product documentation would be
  #    appreciated but is not required.
  # 2. Altered source versions must be plainly marked as such, and must not be
  #    misrepresented as being the original software.
  # 3. This notice may not be removed or altered from any source distribution.
  
  
  """
  Turtle graphics is a popular way for introducing programming to
  kids. It was part of the original Logo programming language developed
  by Wally Feurzig and Seymour Papert in 1966.
  
  Imagine a robotic turtle starting at (0, 0) in the x-y plane. After an ``import turtle``, give it
  the command turtle.forward(15), and it moves (on-screen!) 15 pixels in
  the direction it is facing, drawing a line as it moves. Give it the
  command turtle.right(25), and it rotates in-place 25 degrees clockwise.
  
  By combining together these and similar commands, intricate shapes and
  pictures can easily be drawn.
  
  ----- turtle.py
  
  This module is an extended reimplementation of turtle.py from the
  Python standard distribution up to Python 2.5. (See: http://www.python.org)
  
  It tries to keep the merits of turtle.py and to be (nearly) 100%
  compatible with it. This means in the first place to enable the
  learning programmer to use all the commands, classes and methods
  interactively when using the module from within IDLE run with
  the -n switch.
  
  Roughly it has the following features added:
  
  - Better animation of the turtle movements, especially of turning the
    turtle. So the turtles can more easily be used as a visual feedback
    instrument by the (beginning) programmer.
  
  - Different turtle shapes, gif-images as turtle shapes, user defined
    and user controllable turtle shapes, among them compound
    (multicolored) shapes. Turtle shapes can be stretched and tilted, which
    makes turtles very versatile geometrical objects.
  
  - Fine control over turtle movement and screen updates via delay(),
    and enhanced tracer() and speed() methods.
  
  - Aliases for the most commonly used commands, like fd for forward etc.,
    following the early Logo traditions. This reduces the boring work of
    typing long sequences of commands, which often occur in a natural way
    when kids try to program fancy pictures on their first encounter with
    turtle graphics.
  
  - Turtles now have an undo()-method with configurable undo-buffer.
  
  - Some simple commands/methods for creating event driven programs
    (mouse-, key-, timer-events). Especially useful for programming games.
  
  - A scrollable Canvas class. The default scrollable Canvas can be
    extended interactively as needed while playing around with the turtle(s).
  
  - A TurtleScreen class with methods controlling background color or
    background image, window and canvas size and other properties of the
    TurtleScreen.
  
  - There is a method, setworldcoordinates(), to install a user defined
    coordinate-system for the TurtleScreen.
  
  - The implementation uses a 2-vector class named Vec2D, derived from tuple.
    This class is public, so it can be imported by the application programmer,
    which makes certain types of computations very natural and compact.
  
  - Appearance of the TurtleScreen and the Turtles at startup/import can be
    configured by means of a turtle.cfg configuration file.
    The default configuration mimics the appearance of the old turtle module.
  
  - If configured appropriately the module reads in docstrings from a docstring
    dictionary in some different language, supplied separately  and replaces
    the English ones by those read in. There is a utility function
    write_docstringdict() to write a dictionary with the original (English)
    docstrings to disc, so it can serve as a template for translations.
  
  Behind the scenes there are some features included with possible
  extensions in mind. These will be commented and documented elsewhere.
  
  """
  
  _ver = "turtle 1.1b- - for Python 3.1   -  4. 5. 2009"
  
  # print(_ver)
  
  import tkinter as TK
  import types
  import math
  import time
  import inspect
  import sys
  
  from os.path import isfile, split, join
  from copy import deepcopy
  from tkinter import simpledialog
  
  _tg_classes = ['ScrolledCanvas', 'TurtleScreen', 'Screen',
                 'RawTurtle', 'Turtle', 'RawPen', 'Pen', 'Shape', 'Vec2D']
  _tg_screen_functions = ['addshape', 'bgcolor', 'bgpic', 'bye',
          'clearscreen', 'colormode', 'delay', 'exitonclick', 'getcanvas',
          'getshapes', 'listen', 'mainloop', 'mode', 'numinput',
          'onkey', 'onkeypress', 'onkeyrelease', 'onscreenclick', 'ontimer',
          'register_shape', 'resetscreen', 'screensize', 'setup',
          'setworldcoordinates', 'textinput', 'title', 'tracer', 'turtles', 'update',
          'window_height', 'window_width']
  _tg_turtle_functions = ['back', 'backward', 'begin_fill', 'begin_poly', 'bk',
          'circle', 'clear', 'clearstamp', 'clearstamps', 'clone', 'color',
          'degrees', 'distance', 'dot', 'down', 'end_fill', 'end_poly', 'fd',
          'fillcolor', 'filling', 'forward', 'get_poly', 'getpen', 'getscreen', 'get_shapepoly',
          'getturtle', 'goto', 'heading', 'hideturtle', 'home', 'ht', 'isdown',
          'isvisible', 'left', 'lt', 'onclick', 'ondrag', 'onrelease', 'pd',
          'pen', 'pencolor', 'pendown', 'pensize', 'penup', 'pos', 'position',
          'pu', 'radians', 'right', 'reset', 'resizemode', 'rt',
          'seth', 'setheading', 'setpos', 'setposition', 'settiltangle',
          'setundobuffer', 'setx', 'sety', 'shape', 'shapesize', 'shapetransform', 'shearfactor', 'showturtle',
          'speed', 'st', 'stamp', 'tilt', 'tiltangle', 'towards',
          'turtlesize', 'undo', 'undobufferentries', 'up', 'width',
          'write', 'xcor', 'ycor']
  _tg_utilities = ['write_docstringdict', 'done']
  
  __all__ = (_tg_classes + _tg_screen_functions + _tg_turtle_functions +
             _tg_utilities + ['Terminator']) # + _math_functions)
  
  _alias_list = ['addshape', 'backward', 'bk', 'fd', 'ht', 'lt', 'pd', 'pos',
                 'pu', 'rt', 'seth', 'setpos', 'setposition', 'st',
                 'turtlesize', 'up', 'width']
  
  _CFG = {"width" : 0.5,               # Screen
          "height" : 0.75,
          "canvwidth" : 400,
          "canvheight": 300,
          "leftright": None,
          "topbottom": None,
          "mode": "standard",          # TurtleScreen
          "colormode": 1.0,
          "delay": 10,
          "undobuffersize": 1000,      # RawTurtle
          "shape": "classic",
          "pencolor" : "black",
          "fillcolor" : "black",
          "resizemode" : "noresize",
          "visible" : True,
          "language": "english",        # docstrings
          "exampleturtle": "turtle",
          "examplescreen": "screen",
          "title": "Python Turtle Graphics",
          "using_IDLE": False
         }
  
  def config_dict(filename):
      """Convert content of config-file into dictionary."""
      with open(filename, "r") as f:
          cfglines = f.readlines()
      cfgdict = {}
      for line in cfglines:
          line = line.strip()
          if not line or line.startswith("#"):
              continue
          try:
              key, value = line.split("=")
          except ValueError:
              print("Bad line in config-file %s:\n%s" % (filename,line))
              continue
          key = key.strip()
          value = value.strip()
          if value in ["True", "False", "None", "''", '""']:
              value = eval(value)
          else:
              try:
                  if "." in value:
                      value = float(value)
                  else:
                      value = int(value)
              except ValueError:
                  pass # value need not be converted
          cfgdict[key] = value
      return cfgdict
  
  def readconfig(cfgdict):
      """Read config-files, change configuration-dict accordingly.
  
      If there is a turtle.cfg file in the current working directory,
      read it from there. If this contains an importconfig-value,
      say 'myway', construct filename turtle_mayway.cfg else use
      turtle.cfg and read it from the import-directory, where
      turtle.py is located.
      Update configuration dictionary first according to config-file,
      in the import directory, then according to config-file in the
      current working directory.
      If no config-file is found, the default configuration is used.
      """
      default_cfg = "turtle.cfg"
      cfgdict1 = {}
      cfgdict2 = {}
      if isfile(default_cfg):
          cfgdict1 = config_dict(default_cfg)
      if "importconfig" in cfgdict1:
          default_cfg = "turtle_%s.cfg" % cfgdict1["importconfig"]
      try:
          head, tail = split(__file__)
          cfg_file2 = join(head, default_cfg)
      except Exception:
          cfg_file2 = ""
      if isfile(cfg_file2):
          cfgdict2 = config_dict(cfg_file2)
      _CFG.update(cfgdict2)
      _CFG.update(cfgdict1)
  
  try:
      readconfig(_CFG)
  except Exception:
      print ("No configfile read, reason unknown")
  
  
  class Vec2D(tuple):
      """A 2 dimensional vector class, used as a helper class
      for implementing turtle graphics.
      May be useful for turtle graphics programs also.
      Derived from tuple, so a vector is a tuple!
  
      Provides (for a, b vectors, k number):
         a+b vector addition
         a-b vector subtraction
         a*b inner product
         k*a and a*k multiplication with scalar
         |a| absolute value of a
         a.rotate(angle) rotation
      """
      def __new__(cls, x, y):
          return tuple.__new__(cls, (x, y))
      def __add__(self, other):
          return Vec2D(self[0]+other[0], self[1]+other[1])
      def __mul__(self, other):
          if isinstance(other, Vec2D):
              return self[0]*other[0]+self[1]*other[1]
          return Vec2D(self[0]*other, self[1]*other)
      def __rmul__(self, other):
          if isinstance(other, int) or isinstance(other, float):
              return Vec2D(self[0]*other, self[1]*other)
      def __sub__(self, other):
          return Vec2D(self[0]-other[0], self[1]-other[1])
      def __neg__(self):
          return Vec2D(-self[0], -self[1])
      def __abs__(self):
          return (self[0]**2 + self[1]**2)**0.5
      def rotate(self, angle):
          """rotate self counterclockwise by angle
          """
          perp = Vec2D(-self[1], self[0])
          angle = angle * math.pi / 180.0
          c, s = math.cos(angle), math.sin(angle)
          return Vec2D(self[0]*c+perp[0]*s, self[1]*c+perp[1]*s)
      def __getnewargs__(self):
          return (self[0], self[1])
      def __repr__(self):
          return "(%.2f,%.2f)" % self
  
  
  ##############################################################################
  ### From here up to line    : Tkinter - Interface for turtle.py            ###
  ### May be replaced by an interface to some different graphics toolkit     ###
  ##############################################################################
  
  ## helper functions for Scrolled Canvas, to forward Canvas-methods
  ## to ScrolledCanvas class
  
  def __methodDict(cls, _dict):
      """helper function for Scrolled Canvas"""
      baseList = list(cls.__bases__)
      baseList.reverse()
      for _super in baseList:
          __methodDict(_super, _dict)
      for key, value in cls.__dict__.items():
          if type(value) == types.FunctionType:
              _dict[key] = value
  
  def __methods(cls):
      """helper function for Scrolled Canvas"""
      _dict = {}
      __methodDict(cls, _dict)
      return _dict.keys()
  
  __stringBody = (
      'def %(method)s(self, *args, **kw): return ' +
      'self.%(attribute)s.%(method)s(*args, **kw)')
  
  def __forwardmethods(fromClass, toClass, toPart, exclude = ()):
      ### MANY CHANGES ###
      _dict_1 = {}
      __methodDict(toClass, _dict_1)
      _dict = {}
      mfc = __methods(fromClass)
      for ex in _dict_1.keys():
          if ex[:1] == '_' or ex[-1:] == '_' or ex in exclude or ex in mfc:
              pass
          else:
              _dict[ex] = _dict_1[ex]
  
      for method, func in _dict.items():
          d = {'method': method, 'func': func}
          if isinstance(toPart, str):
              execString = \
                  __stringBody % {'method' : method, 'attribute' : toPart}
          exec(execString, d)
          setattr(fromClass, method, d[method])   ### NEWU!
  
  
  class ScrolledCanvas(TK.Frame):
      """Modeled after the scrolled canvas class from Grayons's Tkinter book.
  
      Used as the default canvas, which pops up automatically when
      using turtle graphics functions or the Turtle class.
      """
      def __init__(self, master, width=500, height=350,
                                            canvwidth=600, canvheight=500):
          TK.Frame.__init__(self, master, width=width, height=height)
          self._rootwindow = self.winfo_toplevel()
          self.width, self.height = width, height
          self.canvwidth, self.canvheight = canvwidth, canvheight
          self.bg = "white"
          self._canvas = TK.Canvas(master, width=width, height=height,
                                   bg=self.bg, relief=TK.SUNKEN, borderwidth=2)
          self.hscroll = TK.Scrollbar(master, command=self._canvas.xview,
                                      orient=TK.HORIZONTAL)
          self.vscroll = TK.Scrollbar(master, command=self._canvas.yview)
          self._canvas.configure(xscrollcommand=self.hscroll.set,
                                 yscrollcommand=self.vscroll.set)
          self.rowconfigure(0, weight=1, minsize=0)
          self.columnconfigure(0, weight=1, minsize=0)
          self._canvas.grid(padx=1, in_ = self, pady=1, row=0,
                  column=0, rowspan=1, columnspan=1, sticky='news')
          self.vscroll.grid(padx=1, in_ = self, pady=1, row=0,
                  column=1, rowspan=1, columnspan=1, sticky='news')
          self.hscroll.grid(padx=1, in_ = self, pady=1, row=1,
                  column=0, rowspan=1, columnspan=1, sticky='news')
          self.reset()
          self._rootwindow.bind('<Configure>', self.onResize)
  
      def reset(self, canvwidth=None, canvheight=None, bg = None):
          """Adjust canvas and scrollbars according to given canvas size."""
          if canvwidth:
              self.canvwidth = canvwidth
          if canvheight:
              self.canvheight = canvheight
          if bg:
              self.bg = bg
          self._canvas.config(bg=bg,
                          scrollregion=(-self.canvwidth//2, -self.canvheight//2,
                                         self.canvwidth//2, self.canvheight//2))
          self._canvas.xview_moveto(0.5*(self.canvwidth - self.width + 30) /
                                                                 self.canvwidth)
          self._canvas.yview_moveto(0.5*(self.canvheight- self.height + 30) /
                                                                self.canvheight)
          self.adjustScrolls()
  
  
      def adjustScrolls(self):
          """ Adjust scrollbars according to window- and canvas-size.
          """
          cwidth = self._canvas.winfo_width()
          cheight = self._canvas.winfo_height()
          self._canvas.xview_moveto(0.5*(self.canvwidth-cwidth)/self.canvwidth)
          self._canvas.yview_moveto(0.5*(self.canvheight-cheight)/self.canvheight)
          if cwidth < self.canvwidth or cheight < self.canvheight:
              self.hscroll.grid(padx=1, in_ = self, pady=1, row=1,
                                column=0, rowspan=1, columnspan=1, sticky='news')
              self.vscroll.grid(padx=1, in_ = self, pady=1, row=0,
                                column=1, rowspan=1, columnspan=1, sticky='news')
          else:
              self.hscroll.grid_forget()
              self.vscroll.grid_forget()
  
      def onResize(self, event):
          """self-explanatory"""
          self.adjustScrolls()
  
      def bbox(self, *args):
          """ 'forward' method, which canvas itself has inherited...
          """
          return self._canvas.bbox(*args)
  
      def cget(self, *args, **kwargs):
          """ 'forward' method, which canvas itself has inherited...
          """
          return self._canvas.cget(*args, **kwargs)
  
      def config(self, *args, **kwargs):
          """ 'forward' method, which canvas itself has inherited...
          """
          self._canvas.config(*args, **kwargs)
  
      def bind(self, *args, **kwargs):
          """ 'forward' method, which canvas itself has inherited...
          """
          self._canvas.bind(*args, **kwargs)
  
      def unbind(self, *args, **kwargs):
          """ 'forward' method, which canvas itself has inherited...
          """
          self._canvas.unbind(*args, **kwargs)
  
      def focus_force(self):
          """ 'forward' method, which canvas itself has inherited...
          """
          self._canvas.focus_force()
  
  __forwardmethods(ScrolledCanvas, TK.Canvas, '_canvas')
  
  
  class _Root(TK.Tk):
      """Root class for Screen based on Tkinter."""
      def __init__(self):
          TK.Tk.__init__(self)
  
      def setupcanvas(self, width, height, cwidth, cheight):
          self._canvas = ScrolledCanvas(self, width, height, cwidth, cheight)
          self._canvas.pack(expand=1, fill="both")
  
      def _getcanvas(self):
          return self._canvas
  
      def set_geometry(self, width, height, startx, starty):
          self.geometry("%dx%d%+d%+d"%(width, height, startx, starty))
  
      def ondestroy(self, destroy):
          self.wm_protocol("WM_DELETE_WINDOW", destroy)
  
      def win_width(self):
          return self.winfo_screenwidth()
  
      def win_height(self):
          return self.winfo_screenheight()
  
  Canvas = TK.Canvas
  
  
  class TurtleScreenBase(object):
      """Provide the basic graphics functionality.
         Interface between Tkinter and turtle.py.
  
         To port turtle.py to some different graphics toolkit
         a corresponding TurtleScreenBase class has to be implemented.
      """
  
      @staticmethod
      def _blankimage():
          """return a blank image object
          """
          img = TK.PhotoImage(width=1, height=1)
          img.blank()
          return img
  
      @staticmethod
      def _image(filename):
          """return an image object containing the
          imagedata from a gif-file named filename.
          """
          return TK.PhotoImage(file=filename)
  
      def __init__(self, cv):
          self.cv = cv
          if isinstance(cv, ScrolledCanvas):
              w = self.cv.canvwidth
              h = self.cv.canvheight
          else:  # expected: ordinary TK.Canvas
              w = int(self.cv.cget("width"))
              h = int(self.cv.cget("height"))
              self.cv.config(scrollregion = (-w//2, -h//2, w//2, h//2 ))
          self.canvwidth = w
          self.canvheight = h
          self.xscale = self.yscale = 1.0
  
      def _createpoly(self):
          """Create an invisible polygon item on canvas self.cv)
          """
          return self.cv.create_polygon((0, 0, 0, 0, 0, 0), fill="", outline="")
  
      def _drawpoly(self, polyitem, coordlist, fill=None,
                    outline=None, width=None, top=False):
          """Configure polygonitem polyitem according to provided
          arguments:
          coordlist is sequence of coordinates
          fill is filling color
          outline is outline color
          top is a boolean value, which specifies if polyitem
          will be put on top of the canvas' displaylist so it
          will not be covered by other items.
          """
          cl = []
          for x, y in coordlist:
              cl.append(x * self.xscale)
              cl.append(-y * self.yscale)
          self.cv.coords(polyitem, *cl)
          if fill is not None:
              self.cv.itemconfigure(polyitem, fill=fill)
          if outline is not None:
              self.cv.itemconfigure(polyitem, outline=outline)
          if width is not None:
              self.cv.itemconfigure(polyitem, width=width)
          if top:
              self.cv.tag_raise(polyitem)
  
      def _createline(self):
          """Create an invisible line item on canvas self.cv)
          """
          return self.cv.create_line(0, 0, 0, 0, fill="", width=2,
                                     capstyle = TK.ROUND)
  
      def _drawline(self, lineitem, coordlist=None,
                    fill=None, width=None, top=False):
          """Configure lineitem according to provided arguments:
          coordlist is sequence of coordinates
          fill is drawing color
          width is width of drawn line.
          top is a boolean value, which specifies if polyitem
          will be put on top of the canvas' displaylist so it
          will not be covered by other items.
          """
          if coordlist is not None:
              cl = []
              for x, y in coordlist:
                  cl.append(x * self.xscale)
                  cl.append(-y * self.yscale)
              self.cv.coords(lineitem, *cl)
          if fill is not None:
              self.cv.itemconfigure(lineitem, fill=fill)
          if width is not None:
              self.cv.itemconfigure(lineitem, width=width)
          if top:
              self.cv.tag_raise(lineitem)
  
      def _delete(self, item):
          """Delete graphics item from canvas.
          If item is"all" delete all graphics items.
          """
          self.cv.delete(item)
  
      def _update(self):
          """Redraw graphics items on canvas
          """
          self.cv.update()
  
      def _delay(self, delay):
          """Delay subsequent canvas actions for delay ms."""
          self.cv.after(delay)
  
      def _iscolorstring(self, color):
          """Check if the string color is a legal Tkinter color string.
          """
          try:
              rgb = self.cv.winfo_rgb(color)
              ok = True
          except TK.TclError:
              ok = False
          return ok
  
      def _bgcolor(self, color=None):
          """Set canvas' backgroundcolor if color is not None,
          else return backgroundcolor."""
          if color is not None:
              self.cv.config(bg = color)
              self._update()
          else:
              return self.cv.cget("bg")
  
      def _write(self, pos, txt, align, font, pencolor):
          """Write txt at pos in canvas with specified font
          and color.
          Return text item and x-coord of right bottom corner
          of text's bounding box."""
          x, y = pos
          x = x * self.xscale
          y = y * self.yscale
          anchor = {"left":"sw", "center":"s", "right":"se" }
          item = self.cv.create_text(x-1, -y, text = txt, anchor = anchor[align],
                                          fill = pencolor, font = font)
          x0, y0, x1, y1 = self.cv.bbox(item)
          self.cv.update()
          return item, x1-1
  
  ##    def _dot(self, pos, size, color):
  ##        """may be implemented for some other graphics toolkit"""
  
      def _onclick(self, item, fun, num=1, add=None):
          """Bind fun to mouse-click event on turtle.
          fun must be a function with two arguments, the coordinates
          of the clicked point on the canvas.
          num, the number of the mouse-button defaults to 1
          """
          if fun is None:
              self.cv.tag_unbind(item, "<Button-%s>" % num)
          else:
              def eventfun(event):
                  x, y = (self.cv.canvasx(event.x)/self.xscale,
                          -self.cv.canvasy(event.y)/self.yscale)
                  fun(x, y)
              self.cv.tag_bind(item, "<Button-%s>" % num, eventfun, add)
  
      def _onrelease(self, item, fun, num=1, add=None):
          """Bind fun to mouse-button-release event on turtle.
          fun must be a function with two arguments, the coordinates
          of the point on the canvas where mouse button is released.
          num, the number of the mouse-button defaults to 1
  
          If a turtle is clicked, first _onclick-event will be performed,
          then _onscreensclick-event.
          """
          if fun is None:
              self.cv.tag_unbind(item, "<Button%s-ButtonRelease>" % num)
          else:
              def eventfun(event):
                  x, y = (self.cv.canvasx(event.x)/self.xscale,
                          -self.cv.canvasy(event.y)/self.yscale)
                  fun(x, y)
              self.cv.tag_bind(item, "<Button%s-ButtonRelease>" % num,
                               eventfun, add)
  
      def _ondrag(self, item, fun, num=1, add=None):
          """Bind fun to mouse-move-event (with pressed mouse button) on turtle.
          fun must be a function with two arguments, the coordinates of the
          actual mouse position on the canvas.
          num, the number of the mouse-button defaults to 1
  
          Every sequence of mouse-move-events on a turtle is preceded by a
          mouse-click event on that turtle.
          """
          if fun is None:
              self.cv.tag_unbind(item, "<Button%s-Motion>" % num)
          else:
              def eventfun(event):
                  try:
                      x, y = (self.cv.canvasx(event.x)/self.xscale,
                             -self.cv.canvasy(event.y)/self.yscale)
                      fun(x, y)
                  except Exception:
                      pass
              self.cv.tag_bind(item, "<Button%s-Motion>" % num, eventfun, add)
  
      def _onscreenclick(self, fun, num=1, add=None):
          """Bind fun to mouse-click event on canvas.
          fun must be a function with two arguments, the coordinates
          of the clicked point on the canvas.
          num, the number of the mouse-button defaults to 1
  
          If a turtle is clicked, first _onclick-event will be performed,
          then _onscreensclick-event.
          """
          if fun is None:
              self.cv.unbind("<Button-%s>" % num)
          else:
              def eventfun(event):
                  x, y = (self.cv.canvasx(event.x)/self.xscale,
                          -self.cv.canvasy(event.y)/self.yscale)
                  fun(x, y)
              self.cv.bind("<Button-%s>" % num, eventfun, add)
  
      def _onkeyrelease(self, fun, key):
          """Bind fun to key-release event of key.
          Canvas must have focus. See method listen
          """
          if fun is None:
              self.cv.unbind("<KeyRelease-%s>" % key, None)
          else:
              def eventfun(event):
                  fun()
              self.cv.bind("<KeyRelease-%s>" % key, eventfun)
  
      def _onkeypress(self, fun, key=None):
          """If key is given, bind fun to key-press event of key.
          Otherwise bind fun to any key-press.
          Canvas must have focus. See method listen.
          """
          if fun is None:
              if key is None:
                  self.cv.unbind("<KeyPress>", None)
              else:
                  self.cv.unbind("<KeyPress-%s>" % key, None)
          else:
              def eventfun(event):
                  fun()
              if key is None:
                  self.cv.bind("<KeyPress>", eventfun)
              else:
                  self.cv.bind("<KeyPress-%s>" % key, eventfun)
  
      def _listen(self):
          """Set focus on canvas (in order to collect key-events)
          """
          self.cv.focus_force()
  
      def _ontimer(self, fun, t):
          """Install a timer, which calls fun after t milliseconds.
          """
          if t == 0:
              self.cv.after_idle(fun)
          else:
              self.cv.after(t, fun)
  
      def _createimage(self, image):
          """Create and return image item on canvas.
          """
          return self.cv.create_image(0, 0, image=image)
  
      def _drawimage(self, item, pos, image):
          """Configure image item as to draw image object
          at position (x,y) on canvas)
          """
          x, y = pos
          self.cv.coords(item, (x * self.xscale, -y * self.yscale))
          self.cv.itemconfig(item, image=image)
  
      def _setbgpic(self, item, image):
          """Configure image item as to draw image object
          at center of canvas. Set item to the first item
          in the displaylist, so it will be drawn below
          any other item ."""
          self.cv.itemconfig(item, image=image)
          self.cv.tag_lower(item)
  
      def _type(self, item):
          """Return 'line' or 'polygon' or 'image' depending on
          type of item.
          """
          return self.cv.type(item)
  
      def _pointlist(self, item):
          """returns list of coordinate-pairs of points of item
          Example (for insiders):
          >>> from turtle import *
          >>> getscreen()._pointlist(getturtle().turtle._item)
          [(0.0, 9.9999999999999982), (0.0, -9.9999999999999982),
          (9.9999999999999982, 0.0)]
          >>> """
          cl = self.cv.coords(item)
          pl = [(cl[i], -cl[i+1]) for i in range(0, len(cl), 2)]
          return  pl
  
      def _setscrollregion(self, srx1, sry1, srx2, sry2):
          self.cv.config(scrollregion=(srx1, sry1, srx2, sry2))
  
      def _rescale(self, xscalefactor, yscalefactor):
          items = self.cv.find_all()
          for item in items:
              coordinates = list(self.cv.coords(item))
              newcoordlist = []
              while coordinates:
                  x, y = coordinates[:2]
                  newcoordlist.append(x * xscalefactor)
                  newcoordlist.append(y * yscalefactor)
                  coordinates = coordinates[2:]
              self.cv.coords(item, *newcoordlist)
  
      def _resize(self, canvwidth=None, canvheight=None, bg=None):
          """Resize the canvas the turtles are drawing on. Does
          not alter the drawing window.
          """
          # needs amendment
          if not isinstance(self.cv, ScrolledCanvas):
              return self.canvwidth, self.canvheight
          if canvwidth is canvheight is bg is None:
              return self.cv.canvwidth, self.cv.canvheight
          if canvwidth is not None:
              self.canvwidth = canvwidth
          if canvheight is not None:
              self.canvheight = canvheight
          self.cv.reset(canvwidth, canvheight, bg)
  
      def _window_size(self):
          """ Return the width and height of the turtle window.
          """
          width = self.cv.winfo_width()
          if width <= 1:  # the window isn't managed by a geometry manager
              width = self.cv['width']
          height = self.cv.winfo_height()
          if height <= 1: # the window isn't managed by a geometry manager
              height = self.cv['height']
          return width, height
  
      def mainloop(self):
          """Starts event loop - calling Tkinter's mainloop function.
  
          No argument.
  
          Must be last statement in a turtle graphics program.
          Must NOT be used if a script is run from within IDLE in -n mode
          (No subprocess) - for interactive use of turtle graphics.
  
          Example (for a TurtleScreen instance named screen):
          >>> screen.mainloop()
  
          """
          TK.mainloop()
  
      def textinput(self, title, prompt):
          """Pop up a dialog window for input of a string.
  
          Arguments: title is the title of the dialog window,
          prompt is a text mostly describing what information to input.
  
          Return the string input
          If the dialog is canceled, return None.
  
          Example (for a TurtleScreen instance named screen):
          >>> screen.textinput("NIM", "Name of first player:")
  
          """
          return simpledialog.askstring(title, prompt)
  
      def numinput(self, title, prompt, default=None, minval=None, maxval=None):
          """Pop up a dialog window for input of a number.
  
          Arguments: title is the title of the dialog window,
          prompt is a text mostly describing what numerical information to input.
          default: default value
          minval: minimum value for input
          maxval: maximum value for input
  
          The number input must be in the range minval .. maxval if these are
          given. If not, a hint is issued and the dialog remains open for
          correction. Return the number input.
          If the dialog is canceled,  return None.
  
          Example (for a TurtleScreen instance named screen):
          >>> screen.numinput("Poker", "Your stakes:", 1000, minval=10, maxval=10000)
  
          """
          return simpledialog.askfloat(title, prompt, initialvalue=default,
                                       minvalue=minval, maxvalue=maxval)
  
  
  ##############################################################################
  ###                  End of Tkinter - interface                            ###
  ##############################################################################
  
  
  class Terminator (Exception):
      """Will be raised in TurtleScreen.update, if _RUNNING becomes False.
  
      This stops execution of a turtle graphics script.
      Main purpose: use in the Demo-Viewer turtle.Demo.py.
      """
      pass
  
  
  class TurtleGraphicsError(Exception):
      """Some TurtleGraphics Error
      """
  
  
  class Shape(object):
      """Data structure modeling shapes.
  
      attribute _type is one of "polygon", "image", "compound"
      attribute _data is - depending on _type a poygon-tuple,
      an image or a list constructed using the addcomponent method.
      """
      def __init__(self, type_, data=None):
          self._type = type_
          if type_ == "polygon":
              if isinstance(data, list):
                  data = tuple(data)
          elif type_ == "image":
              if isinstance(data, str):
                  if data.lower().endswith(".gif") and isfile(data):
                      data = TurtleScreen._image(data)
                  # else data assumed to be Photoimage
          elif type_ == "compound":
              data = []
          else:
              raise TurtleGraphicsError("There is no shape type %s" % type_)
          self._data = data
  
      def addcomponent(self, poly, fill, outline=None):
          """Add component to a shape of type compound.
  
          Arguments: poly is a polygon, i. e. a tuple of number pairs.
          fill is the fillcolor of the component,
          outline is the outline color of the component.
  
          call (for a Shapeobject namend s):
          --   s.addcomponent(((0,0), (10,10), (-10,10)), "red", "blue")
  
          Example:
          >>> poly = ((0,0),(10,-5),(0,10),(-10,-5))
          >>> s = Shape("compound")
          >>> s.addcomponent(poly, "red", "blue")
          >>> # .. add more components and then use register_shape()
          """
          if self._type != "compound":
              raise TurtleGraphicsError("Cannot add component to %s Shape"
                                                                  % self._type)
          if outline is None:
              outline = fill
          self._data.append([poly, fill, outline])
  
  
  class Tbuffer(object):
      """Ring buffer used as undobuffer for RawTurtle objects."""
      def __init__(self, bufsize=10):
          self.bufsize = bufsize
          self.buffer = [[None]] * bufsize
          self.ptr = -1
          self.cumulate = False
      def reset(self, bufsize=None):
          if bufsize is None:
              for i in range(self.bufsize):
                  self.buffer[i] = [None]
          else:
              self.bufsize = bufsize
              self.buffer = [[None]] * bufsize
          self.ptr = -1
      def push(self, item):
          if self.bufsize > 0:
              if not self.cumulate:
                  self.ptr = (self.ptr + 1) % self.bufsize
                  self.buffer[self.ptr] = item
              else:
                  self.buffer[self.ptr].append(item)
      def pop(self):
          if self.bufsize > 0:
              item = self.buffer[self.ptr]
              if item is None:
                  return None
              else:
                  self.buffer[self.ptr] = [None]
                  self.ptr = (self.ptr - 1) % self.bufsize
                  return (item)
      def nr_of_items(self):
          return self.bufsize - self.buffer.count([None])
      def __repr__(self):
          return str(self.buffer) + " " + str(self.ptr)
  
  
  
  class TurtleScreen(TurtleScreenBase):
      """Provides screen oriented methods like setbg etc.
  
      Only relies upon the methods of TurtleScreenBase and NOT
      upon components of the underlying graphics toolkit -
      which is Tkinter in this case.
      """
      _RUNNING = True
  
      def __init__(self, cv, mode=_CFG["mode"],
                   colormode=_CFG["colormode"], delay=_CFG["delay"]):
          self._shapes = {
                     "arrow" : Shape("polygon", ((-10,0), (10,0), (0,10))),
                    "turtle" : Shape("polygon", ((0,16), (-2,14), (-1,10), (-4,7),
                                (-7,9), (-9,8), (-6,5), (-7,1), (-5,-3), (-8,-6),
                                (-6,-8), (-4,-5), (0,-7), (4,-5), (6,-8), (8,-6),
                                (5,-3), (7,1), (6,5), (9,8), (7,9), (4,7), (1,10),
                                (2,14))),
                    "circle" : Shape("polygon", ((10,0), (9.51,3.09), (8.09,5.88),
                                (5.88,8.09), (3.09,9.51), (0,10), (-3.09,9.51),
                                (-5.88,8.09), (-8.09,5.88), (-9.51,3.09), (-10,0),
                                (-9.51,-3.09), (-8.09,-5.88), (-5.88,-8.09),
                                (-3.09,-9.51), (-0.00,-10.00), (3.09,-9.51),
                                (5.88,-8.09), (8.09,-5.88), (9.51,-3.09))),
                    "square" : Shape("polygon", ((10,-10), (10,10), (-10,10),
                                (-10,-10))),
                  "triangle" : Shape("polygon", ((10,-5.77), (0,11.55),
                                (-10,-5.77))),
                    "classic": Shape("polygon", ((0,0),(-5,-9),(0,-7),(5,-9))),
                     "blank" : Shape("image", self._blankimage())
                    }
  
          self._bgpics = {"nopic" : ""}
  
          TurtleScreenBase.__init__(self, cv)
          self._mode = mode
          self._delayvalue = delay
          self._colormode = _CFG["colormode"]
          self._keys = []
          self.clear()
          if sys.platform == 'darwin':
              # Force Turtle window to the front on OS X. This is needed because
              # the Turtle window will show behind the Terminal window when you
              # start the demo from the command line.
              rootwindow = cv.winfo_toplevel()
              rootwindow.call('wm', 'attributes', '.', '-topmost', '1')
              rootwindow.call('wm', 'attributes', '.', '-topmost', '0')
  
      def clear(self):
          """Delete all drawings and all turtles from the TurtleScreen.
  
          No argument.
  
          Reset empty TurtleScreen to its initial state: white background,
          no backgroundimage, no eventbindings and tracing on.
  
          Example (for a TurtleScreen instance named screen):
          >>> screen.clear()
  
          Note: this method is not available as function.
          """
          self._delayvalue = _CFG["delay"]
          self._colormode = _CFG["colormode"]
          self._delete("all")
          self._bgpic = self._createimage("")
          self._bgpicname = "nopic"
          self._tracing = 1
          self._updatecounter = 0
          self._turtles = []
          self.bgcolor("white")
          for btn in 1, 2, 3:
              self.onclick(None, btn)
          self.onkeypress(None)
          for key in self._keys[:]:
              self.onkey(None, key)
              self.onkeypress(None, key)
          Turtle._pen = None
  
      def mode(self, mode=None):
          """Set turtle-mode ('standard', 'logo' or 'world') and perform reset.
  
          Optional argument:
          mode -- one of the strings 'standard', 'logo' or 'world'
  
          Mode 'standard' is compatible with turtle.py.
          Mode 'logo' is compatible with most Logo-Turtle-Graphics.
          Mode 'world' uses userdefined 'worldcoordinates'. *Attention*: in
          this mode angles appear distorted if x/y unit-ratio doesn't equal 1.
          If mode is not given, return the current mode.
  
               Mode      Initial turtle heading     positive angles
           ------------|-------------------------|-------------------
            'standard'    to the right (east)       counterclockwise
              'logo'        upward    (north)         clockwise
  
          Examples:
          >>> mode('logo')   # resets turtle heading to north
          >>> mode()
          'logo'
          """
          if mode is None:
              return self._mode
          mode = mode.lower()
          if mode not in ["standard", "logo", "world"]:
              raise TurtleGraphicsError("No turtle-graphics-mode %s" % mode)
          self._mode = mode
          if mode in ["standard", "logo"]:
              self._setscrollregion(-self.canvwidth//2, -self.canvheight//2,
                                         self.canvwidth//2, self.canvheight//2)
              self.xscale = self.yscale = 1.0
          self.reset()
  
      def setworldcoordinates(self, llx, lly, urx, ury):
          """Set up a user defined coordinate-system.
  
          Arguments:
          llx -- a number, x-coordinate of lower left corner of canvas
          lly -- a number, y-coordinate of lower left corner of canvas
          urx -- a number, x-coordinate of upper right corner of canvas
          ury -- a number, y-coordinate of upper right corner of canvas
  
          Set up user coodinat-system and switch to mode 'world' if necessary.
          This performs a screen.reset. If mode 'world' is already active,
          all drawings are redrawn according to the new coordinates.
  
          But ATTENTION: in user-defined coordinatesystems angles may appear
          distorted. (see Screen.mode())
  
          Example (for a TurtleScreen instance named screen):
          >>> screen.setworldcoordinates(-10,-0.5,50,1.5)
          >>> for _ in range(36):
          ...     left(10)
          ...     forward(0.5)
          """
          if self.mode() != "world":
              self.mode("world")
          xspan = float(urx - llx)
          yspan = float(ury - lly)
          wx, wy = self._window_size()
          self.screensize(wx-20, wy-20)
          oldxscale, oldyscale = self.xscale, self.yscale
          self.xscale = self.canvwidth / xspan
          self.yscale = self.canvheight / yspan
          srx1 = llx * self.xscale
          sry1 = -ury * self.yscale
          srx2 = self.canvwidth + srx1
          sry2 = self.canvheight + sry1
          self._setscrollregion(srx1, sry1, srx2, sry2)
          self._rescale(self.xscale/oldxscale, self.yscale/oldyscale)
          self.update()
  
      def register_shape(self, name, shape=None):
          """Adds a turtle shape to TurtleScreen's shapelist.
  
          Arguments:
          (1) name is the name of a gif-file and shape is None.
              Installs the corresponding image shape.
              !! Image-shapes DO NOT rotate when turning the turtle,
              !! so they do not display the heading of the turtle!
          (2) name is an arbitrary string and shape is a tuple
              of pairs of coordinates. Installs the corresponding
              polygon shape
          (3) name is an arbitrary string and shape is a
              (compound) Shape object. Installs the corresponding
              compound shape.
          To use a shape, you have to issue the command shape(shapename).
  
          call: register_shape("turtle.gif")
          --or: register_shape("tri", ((0,0), (10,10), (-10,10)))
  
          Example (for a TurtleScreen instance named screen):
          >>> screen.register_shape("triangle", ((5,-3),(0,5),(-5,-3)))
  
          """
          if shape is None:
              # image
              if name.lower().endswith(".gif"):
                  shape = Shape("image", self._image(name))
              else:
                  raise TurtleGraphicsError("Bad arguments for register_shape.\n"
                                            + "Use  help(register_shape)" )
          elif isinstance(shape, tuple):
              shape = Shape("polygon", shape)
          ## else shape assumed to be Shape-instance
          self._shapes[name] = shape
  
      def _colorstr(self, color):
          """Return color string corresponding to args.
  
          Argument may be a string or a tuple of three
          numbers corresponding to actual colormode,
          i.e. in the range 0<=n<=colormode.
  
          If the argument doesn't represent a color,
          an error is raised.
          """
          if len(color) == 1:
              color = color[0]
          if isinstance(color, str):
              if self._iscolorstring(color) or color == "":
                  return color
              else:
                  raise TurtleGraphicsError("bad color string: %s" % str(color))
          try:
              r, g, b = color
          except (TypeError, ValueError):
              raise TurtleGraphicsError("bad color arguments: %s" % str(color))
          if self._colormode == 1.0:
              r, g, b = [round(255.0*x) for x in (r, g, b)]
          if not ((0 <= r <= 255) and (0 <= g <= 255) and (0 <= b <= 255)):
              raise TurtleGraphicsError("bad color sequence: %s" % str(color))
          return "#%02x%02x%02x" % (r, g, b)
  
      def _color(self, cstr):
          if not cstr.startswith("#"):
              return cstr
          if len(cstr) == 7:
              cl = [int(cstr[i:i+2], 16) for i in (1, 3, 5)]
          elif len(cstr) == 4:
              cl = [16*int(cstr[h], 16) for h in cstr[1:]]
          else:
              raise TurtleGraphicsError("bad colorstring: %s" % cstr)
          return tuple(c * self._colormode/255 for c in cl)
  
      def colormode(self, cmode=None):
          """Return the colormode or set it to 1.0 or 255.
  
          Optional argument:
          cmode -- one of the values 1.0 or 255
  
          r, g, b values of colortriples have to be in range 0..cmode.
  
          Example (for a TurtleScreen instance named screen):
          >>> screen.colormode()
          1.0
          >>> screen.colormode(255)
          >>> pencolor(240,160,80)
          """
          if cmode is None:
              return self._colormode
          if cmode == 1.0:
              self._colormode = float(cmode)
          elif cmode == 255:
              self._colormode = int(cmode)
  
      def reset(self):
          """Reset all Turtles on the Screen to their initial state.
  
          No argument.
  
          Example (for a TurtleScreen instance named screen):
          >>> screen.reset()
          """
          for turtle in self._turtles:
              turtle._setmode(self._mode)
              turtle.reset()
  
      def turtles(self):
          """Return the list of turtles on the screen.
  
          Example (for a TurtleScreen instance named screen):
          >>> screen.turtles()
          [<turtle.Turtle object at 0x00E11FB0>]
          """
          return self._turtles
  
      def bgcolor(self, *args):
          """Set or return backgroundcolor of the TurtleScreen.
  
          Arguments (if given): a color string or three numbers
          in the range 0..colormode or a 3-tuple of such numbers.
  
          Example (for a TurtleScreen instance named screen):
          >>> screen.bgcolor("orange")
          >>> screen.bgcolor()
          'orange'
          >>> screen.bgcolor(0.5,0,0.5)
          >>> screen.bgcolor()
          '#800080'
          """
          if args:
              color = self._colorstr(args)
          else:
              color = None
          color = self._bgcolor(color)
          if color is not None:
              color = self._color(color)
          return color
  
      def tracer(self, n=None, delay=None):
          """Turns turtle animation on/off and set delay for update drawings.
  
          Optional arguments:
          n -- nonnegative  integer
          delay -- nonnegative  integer
  
          If n is given, only each n-th regular screen update is really performed.
          (Can be used to accelerate the drawing of complex graphics.)
          Second arguments sets delay value (see RawTurtle.delay())
  
          Example (for a TurtleScreen instance named screen):
          >>> screen.tracer(8, 25)
          >>> dist = 2
          >>> for i in range(200):
          ...     fd(dist)
          ...     rt(90)
          ...     dist += 2
          """
          if n is None:
              return self._tracing
          self._tracing = int(n)
          self._updatecounter = 0
          if delay is not None:
              self._delayvalue = int(delay)
          if self._tracing:
              self.update()
  
      def delay(self, delay=None):
          """ Return or set the drawing delay in milliseconds.
  
          Optional argument:
          delay -- positive integer
  
          Example (for a TurtleScreen instance named screen):
          >>> screen.delay(15)
          >>> screen.delay()
          15
          """
          if delay is None:
              return self._delayvalue
          self._delayvalue = int(delay)
  
      def _incrementudc(self):
          """Increment update counter."""
          if not TurtleScreen._RUNNING:
              TurtleScreen._RUNNING = True
              raise Terminator
          if self._tracing > 0:
              self._updatecounter += 1
              self._updatecounter %= self._tracing
  
      def update(self):
          """Perform a TurtleScreen update.
          """
          tracing = self._tracing
          self._tracing = True
          for t in self.turtles():
              t._update_data()
              t._drawturtle()
          self._tracing = tracing
          self._update()
  
      def window_width(self):
          """ Return the width of the turtle window.
  
          Example (for a TurtleScreen instance named screen):
          >>> screen.window_width()
          640
          """
          return self._window_size()[0]
  
      def window_height(self):
          """ Return the height of the turtle window.
  
          Example (for a TurtleScreen instance named screen):
          >>> screen.window_height()
          480
          """
          return self._window_size()[1]
  
      def getcanvas(self):
          """Return the Canvas of this TurtleScreen.
  
          No argument.
  
          Example (for a Screen instance named screen):
          >>> cv = screen.getcanvas()
          >>> cv
          <turtle.ScrolledCanvas instance at 0x010742D8>
          """
          return self.cv
  
      def getshapes(self):
          """Return a list of names of all currently available turtle shapes.
  
          No argument.
  
          Example (for a TurtleScreen instance named screen):
          >>> screen.getshapes()
          ['arrow', 'blank', 'circle', ... , 'turtle']
          """
          return sorted(self._shapes.keys())
  
      def onclick(self, fun, btn=1, add=None):
          """Bind fun to mouse-click event on canvas.
  
          Arguments:
          fun -- a function with two arguments, the coordinates of the
                 clicked point on the canvas.
          btn -- the number of the mouse-button, defaults to 1
  
          Example (for a TurtleScreen instance named screen)
  
          >>> screen.onclick(goto)
          >>> # Subsequently clicking into the TurtleScreen will
          >>> # make the turtle move to the clicked point.
          >>> screen.onclick(None)
          """
          self._onscreenclick(fun, btn, add)
  
      def onkey(self, fun, key):
          """Bind fun to key-release event of key.
  
          Arguments:
          fun -- a function with no arguments
          key -- a string: key (e.g. "a") or key-symbol (e.g. "space")
  
          In order to be able to register key-events, TurtleScreen
          must have focus. (See method listen.)
  
          Example (for a TurtleScreen instance named screen):
  
          >>> def f():
          ...     fd(50)
          ...     lt(60)
          ...
          >>> screen.onkey(f, "Up")
          >>> screen.listen()
  
          Subsequently the turtle can be moved by repeatedly pressing
          the up-arrow key, consequently drawing a hexagon
  
          """
          if fun is None:
              if key in self._keys:
                  self._keys.remove(key)
          elif key not in self._keys:
              self._keys.append(key)
          self._onkeyrelease(fun, key)
  
      def onkeypress(self, fun, key=None):
          """Bind fun to key-press event of key if key is given,
          or to any key-press-event if no key is given.
  
          Arguments:
          fun -- a function with no arguments
          key -- a string: key (e.g. "a") or key-symbol (e.g. "space")
  
          In order to be able to register key-events, TurtleScreen
          must have focus. (See method listen.)
  
          Example (for a TurtleScreen instance named screen
          and a Turtle instance named turtle):
  
          >>> def f():
          ...     fd(50)
          ...     lt(60)
          ...
          >>> screen.onkeypress(f, "Up")
          >>> screen.listen()
  
          Subsequently the turtle can be moved by repeatedly pressing
          the up-arrow key, or by keeping pressed the up-arrow key.
          consequently drawing a hexagon.
          """
          if fun is None:
              if key in self._keys:
                  self._keys.remove(key)
          elif key is not None and key not in self._keys:
              self._keys.append(key)
          self._onkeypress(fun, key)
  
      def listen(self, xdummy=None, ydummy=None):
          """Set focus on TurtleScreen (in order to collect key-events)
  
          No arguments.
          Dummy arguments are provided in order
          to be able to pass listen to the onclick method.
  
          Example (for a TurtleScreen instance named screen):
          >>> screen.listen()
          """
          self._listen()
  
      def ontimer(self, fun, t=0):
          """Install a timer, which calls fun after t milliseconds.
  
          Arguments:
          fun -- a function with no arguments.
          t -- a number >= 0
  
          Example (for a TurtleScreen instance named screen):
  
          >>> running = True
          >>> def f():
          ...     if running:
          ...             fd(50)
          ...             lt(60)
          ...             screen.ontimer(f, 250)
          ...
          >>> f()   # makes the turtle marching around
          >>> running = False
          """
          self._ontimer(fun, t)
  
      def bgpic(self, picname=None):
          """Set background image or return name of current backgroundimage.
  
          Optional argument:
          picname -- a string, name of a gif-file or "nopic".
  
          If picname is a filename, set the corresponding image as background.
          If picname is "nopic", delete backgroundimage, if present.
          If picname is None, return the filename of the current backgroundimage.
  
          Example (for a TurtleScreen instance named screen):
          >>> screen.bgpic()
          'nopic'
          >>> screen.bgpic("landscape.gif")
          >>> screen.bgpic()
          'landscape.gif'
          """
          if picname is None:
              return self._bgpicname
          if picname not in self._bgpics:
              self._bgpics[picname] = self._image(picname)
          self._setbgpic(self._bgpic, self._bgpics[picname])
          self._bgpicname = picname
  
      def screensize(self, canvwidth=None, canvheight=None, bg=None):
          """Resize the canvas the turtles are drawing on.
  
          Optional arguments:
          canvwidth -- positive integer, new width of canvas in pixels
          canvheight --  positive integer, new height of canvas in pixels
          bg -- colorstring or color-tuple, new backgroundcolor
          If no arguments are given, return current (canvaswidth, canvasheight)
  
          Do not alter the drawing window. To observe hidden parts of
          the canvas use the scrollbars. (Can make visible those parts
          of a drawing, which were outside the canvas before!)
  
          Example (for a Turtle instance named turtle):
          >>> turtle.screensize(2000,1500)
          >>> # e.g. to search for an erroneously escaped turtle ;-)
          """
          return self._resize(canvwidth, canvheight, bg)
  
      onscreenclick = onclick
      resetscreen = reset
      clearscreen = clear
      addshape = register_shape
      onkeyrelease = onkey
  
  class TNavigator(object):
      """Navigation part of the RawTurtle.
      Implements methods for turtle movement.
      """
      START_ORIENTATION = {
          "standard": Vec2D(1.0, 0.0),
          "world"   : Vec2D(1.0, 0.0),
          "logo"    : Vec2D(0.0, 1.0)  }
      DEFAULT_MODE = "standard"
      DEFAULT_ANGLEOFFSET = 0
      DEFAULT_ANGLEORIENT = 1
  
      def __init__(self, mode=DEFAULT_MODE):
          self._angleOffset = self.DEFAULT_ANGLEOFFSET
          self._angleOrient = self.DEFAULT_ANGLEORIENT
          self._mode = mode
          self.undobuffer = None
          self.degrees()
          self._mode = None
          self._setmode(mode)
          TNavigator.reset(self)
  
      def reset(self):
          """reset turtle to its initial values
  
          Will be overwritten by parent class
          """
          self._position = Vec2D(0.0, 0.0)
          self._orient =  TNavigator.START_ORIENTATION[self._mode]
  
      def _setmode(self, mode=None):
          """Set turtle-mode to 'standard', 'world' or 'logo'.
          """
          if mode is None:
              return self._mode
          if mode not in ["standard", "logo", "world"]:
              return
          self._mode = mode
          if mode in ["standard", "world"]:
              self._angleOffset = 0
              self._angleOrient = 1
          else: # mode == "logo":
              self._angleOffset = self._fullcircle/4.
              self._angleOrient = -1
  
      def _setDegreesPerAU(self, fullcircle):
          """Helper function for degrees() and radians()"""
          self._fullcircle = fullcircle
          self._degreesPerAU = 360/fullcircle
          if self._mode == "standard":
              self._angleOffset = 0
          else:
              self._angleOffset = fullcircle/4.
  
      def degrees(self, fullcircle=360.0):
          """ Set angle measurement units to degrees.
  
          Optional argument:
          fullcircle -  a number
  
          Set angle measurement units, i. e. set number
          of 'degrees' for a full circle. Default value is
          360 degrees.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.left(90)
          >>> turtle.heading()
          90
  
          Change angle measurement unit to grad (also known as gon,
          grade, or gradian and equals 1/100-th of the right angle.)
          >>> turtle.degrees(400.0)
          >>> turtle.heading()
          100
  
          """
          self._setDegreesPerAU(fullcircle)
  
      def radians(self):
          """ Set the angle measurement units to radians.
  
          No arguments.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.heading()
          90
          >>> turtle.radians()
          >>> turtle.heading()
          1.5707963267948966
          """
          self._setDegreesPerAU(2*math.pi)
  
      def _go(self, distance):
          """move turtle forward by specified distance"""
          ende = self._position + self._orient * distance
          self._goto(ende)
  
      def _rotate(self, angle):
          """Turn turtle counterclockwise by specified angle if angle > 0."""
          angle *= self._degreesPerAU
          self._orient = self._orient.rotate(angle)
  
      def _goto(self, end):
          """move turtle to position end."""
          self._position = end
  
      def forward(self, distance):
          """Move the turtle forward by the specified distance.
  
          Aliases: forward | fd
  
          Argument:
          distance -- a number (integer or float)
  
          Move the turtle forward by the specified distance, in the direction
          the turtle is headed.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.position()
          (0.00, 0.00)
          >>> turtle.forward(25)
          >>> turtle.position()
          (25.00,0.00)
          >>> turtle.forward(-75)
          >>> turtle.position()
          (-50.00,0.00)
          """
          self._go(distance)
  
      def back(self, distance):
          """Move the turtle backward by distance.
  
          Aliases: back | backward | bk
  
          Argument:
          distance -- a number
  
          Move the turtle backward by distance ,opposite to the direction the
          turtle is headed. Do not change the turtle's heading.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.position()
          (0.00, 0.00)
          >>> turtle.backward(30)
          >>> turtle.position()
          (-30.00, 0.00)
          """
          self._go(-distance)
  
      def right(self, angle):
          """Turn turtle right by angle units.
  
          Aliases: right | rt
  
          Argument:
          angle -- a number (integer or float)
  
          Turn turtle right by angle units. (Units are by default degrees,
          but can be set via the degrees() and radians() functions.)
          Angle orientation depends on mode. (See this.)
  
          Example (for a Turtle instance named turtle):
          >>> turtle.heading()
          22.0
          >>> turtle.right(45)
          >>> turtle.heading()
          337.0
          """
          self._rotate(-angle)
  
      def left(self, angle):
          """Turn turtle left by angle units.
  
          Aliases: left | lt
  
          Argument:
          angle -- a number (integer or float)
  
          Turn turtle left by angle units. (Units are by default degrees,
          but can be set via the degrees() and radians() functions.)
          Angle orientation depends on mode. (See this.)
  
          Example (for a Turtle instance named turtle):
          >>> turtle.heading()
          22.0
          >>> turtle.left(45)
          >>> turtle.heading()
          67.0
          """
          self._rotate(angle)
  
      def pos(self):
          """Return the turtle's current location (x,y), as a Vec2D-vector.
  
          Aliases: pos | position
  
          No arguments.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.pos()
          (0.00, 240.00)
          """
          return self._position
  
      def xcor(self):
          """ Return the turtle's x coordinate.
  
          No arguments.
  
          Example (for a Turtle instance named turtle):
          >>> reset()
          >>> turtle.left(60)
          >>> turtle.forward(100)
          >>> print turtle.xcor()
          50.0
          """
          return self._position[0]
  
      def ycor(self):
          """ Return the turtle's y coordinate
          ---
          No arguments.
  
          Example (for a Turtle instance named turtle):
          >>> reset()
          >>> turtle.left(60)
          >>> turtle.forward(100)
          >>> print turtle.ycor()
          86.6025403784
          """
          return self._position[1]
  
  
      def goto(self, x, y=None):
          """Move turtle to an absolute position.
  
          Aliases: setpos | setposition | goto:
  
          Arguments:
          x -- a number      or     a pair/vector of numbers
          y -- a number             None
  
          call: goto(x, y)         # two coordinates
          --or: goto((x, y))       # a pair (tuple) of coordinates
          --or: goto(vec)          # e.g. as returned by pos()
  
          Move turtle to an absolute position. If the pen is down,
          a line will be drawn. The turtle's orientation does not change.
  
          Example (for a Turtle instance named turtle):
          >>> tp = turtle.pos()
          >>> tp
          (0.00, 0.00)
          >>> turtle.setpos(60,30)
          >>> turtle.pos()
          (60.00,30.00)
          >>> turtle.setpos((20,80))
          >>> turtle.pos()
          (20.00,80.00)
          >>> turtle.setpos(tp)
          >>> turtle.pos()
          (0.00,0.00)
          """
          if y is None:
              self._goto(Vec2D(*x))
          else:
              self._goto(Vec2D(x, y))
  
      def home(self):
          """Move turtle to the origin - coordinates (0,0).
  
          No arguments.
  
          Move turtle to the origin - coordinates (0,0) and set its
          heading to its start-orientation (which depends on mode).
  
          Example (for a Turtle instance named turtle):
          >>> turtle.home()
          """
          self.goto(0, 0)
          self.setheading(0)
  
      def setx(self, x):
          """Set the turtle's first coordinate to x
  
          Argument:
          x -- a number (integer or float)
  
          Set the turtle's first coordinate to x, leave second coordinate
          unchanged.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.position()
          (0.00, 240.00)
          >>> turtle.setx(10)
          >>> turtle.position()
          (10.00, 240.00)
          """
          self._goto(Vec2D(x, self._position[1]))
  
      def sety(self, y):
          """Set the turtle's second coordinate to y
  
          Argument:
          y -- a number (integer or float)
  
          Set the turtle's first coordinate to x, second coordinate remains
          unchanged.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.position()
          (0.00, 40.00)
          >>> turtle.sety(-10)
          >>> turtle.position()
          (0.00, -10.00)
          """
          self._goto(Vec2D(self._position[0], y))
  
      def distance(self, x, y=None):
          """Return the distance from the turtle to (x,y) in turtle step units.
  
          Arguments:
          x -- a number   or  a pair/vector of numbers   or   a turtle instance
          y -- a number       None                            None
  
          call: distance(x, y)         # two coordinates
          --or: distance((x, y))       # a pair (tuple) of coordinates
          --or: distance(vec)          # e.g. as returned by pos()
          --or: distance(mypen)        # where mypen is another turtle
  
          Example (for a Turtle instance named turtle):
          >>> turtle.pos()
          (0.00, 0.00)
          >>> turtle.distance(30,40)
          50.0
          >>> pen = Turtle()
          >>> pen.forward(77)
          >>> turtle.distance(pen)
          77.0
          """
          if y is not None:
              pos = Vec2D(x, y)
          if isinstance(x, Vec2D):
              pos = x
          elif isinstance(x, tuple):
              pos = Vec2D(*x)
          elif isinstance(x, TNavigator):
              pos = x._position
          return abs(pos - self._position)
  
      def towards(self, x, y=None):
          """Return the angle of the line from the turtle's position to (x, y).
  
          Arguments:
          x -- a number   or  a pair/vector of numbers   or   a turtle instance
          y -- a number       None                            None
  
          call: distance(x, y)         # two coordinates
          --or: distance((x, y))       # a pair (tuple) of coordinates
          --or: distance(vec)          # e.g. as returned by pos()
          --or: distance(mypen)        # where mypen is another turtle
  
          Return the angle, between the line from turtle-position to position
          specified by x, y and the turtle's start orientation. (Depends on
          modes - "standard" or "logo")
  
          Example (for a Turtle instance named turtle):
          >>> turtle.pos()
          (10.00, 10.00)
          >>> turtle.towards(0,0)
          225.0
          """
          if y is not None:
              pos = Vec2D(x, y)
          if isinstance(x, Vec2D):
              pos = x
          elif isinstance(x, tuple):
              pos = Vec2D(*x)
          elif isinstance(x, TNavigator):
              pos = x._position
          x, y = pos - self._position
          result = round(math.atan2(y, x)*180.0/math.pi, 10) % 360.0
          result /= self._degreesPerAU
          return (self._angleOffset + self._angleOrient*result) % self._fullcircle
  
      def heading(self):
          """ Return the turtle's current heading.
  
          No arguments.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.left(67)
          >>> turtle.heading()
          67.0
          """
          x, y = self._orient
          result = round(math.atan2(y, x)*180.0/math.pi, 10) % 360.0
          result /= self._degreesPerAU
          return (self._angleOffset + self._angleOrient*result) % self._fullcircle
  
      def setheading(self, to_angle):
          """Set the orientation of the turtle to to_angle.
  
          Aliases:  setheading | seth
  
          Argument:
          to_angle -- a number (integer or float)
  
          Set the orientation of the turtle to to_angle.
          Here are some common directions in degrees:
  
           standard - mode:          logo-mode:
          -------------------|--------------------
             0 - east                0 - north
            90 - north              90 - east
           180 - west              180 - south
           270 - south             270 - west
  
          Example (for a Turtle instance named turtle):
          >>> turtle.setheading(90)
          >>> turtle.heading()
          90
          """
          angle = (to_angle - self.heading())*self._angleOrient
          full = self._fullcircle
          angle = (angle+full/2.)%full - full/2.
          self._rotate(angle)
  
      def circle(self, radius, extent = None, steps = None):
          """ Draw a circle with given radius.
  
          Arguments:
          radius -- a number
          extent (optional) -- a number
          steps (optional) -- an integer
  
          Draw a circle with given radius. The center is radius units left
          of the turtle; extent - an angle - determines which part of the
          circle is drawn. If extent is not given, draw the entire circle.
          If extent is not a full circle, one endpoint of the arc is the
          current pen position. Draw the arc in counterclockwise direction
          if radius is positive, otherwise in clockwise direction. Finally
          the direction of the turtle is changed by the amount of extent.
  
          As the circle is approximated by an inscribed regular polygon,
          steps determines the number of steps to use. If not given,
          it will be calculated automatically. Maybe used to draw regular
          polygons.
  
          call: circle(radius)                  # full circle
          --or: circle(radius, extent)          # arc
          --or: circle(radius, extent, steps)
          --or: circle(radius, steps=6)         # 6-sided polygon
  
          Example (for a Turtle instance named turtle):
          >>> turtle.circle(50)
          >>> turtle.circle(120, 180)  # semicircle
          """
          if self.undobuffer:
              self.undobuffer.push(["seq"])
              self.undobuffer.cumulate = True
          speed = self.speed()
          if extent is None:
              extent = self._fullcircle
          if steps is None:
              frac = abs(extent)/self._fullcircle
              steps = 1+int(min(11+abs(radius)/6.0, 59.0)*frac)
          w = 1.0 * extent / steps
          w2 = 0.5 * w
          l = 2.0 * radius * math.sin(w2*math.pi/180.0*self._degreesPerAU)
          if radius < 0:
              l, w, w2 = -l, -w, -w2
          tr = self._tracer()
          dl = self._delay()
          if speed == 0:
              self._tracer(0, 0)
          else:
              self.speed(0)
          self._rotate(w2)
          for i in range(steps):
              self.speed(speed)
              self._go(l)
              self.speed(0)
              self._rotate(w)
          self._rotate(-w2)
          if speed == 0:
              self._tracer(tr, dl)
          self.speed(speed)
          if self.undobuffer:
              self.undobuffer.cumulate = False
  
  ## three dummy methods to be implemented by child class:
  
      def speed(self, s=0):
          """dummy method - to be overwritten by child class"""
      def _tracer(self, a=None, b=None):
          """dummy method - to be overwritten by child class"""
      def _delay(self, n=None):
          """dummy method - to be overwritten by child class"""
  
      fd = forward
      bk = back
      backward = back
      rt = right
      lt = left
      position = pos
      setpos = goto
      setposition = goto
      seth = setheading
  
  
  class TPen(object):
      """Drawing part of the RawTurtle.
      Implements drawing properties.
      """
      def __init__(self, resizemode=_CFG["resizemode"]):
          self._resizemode = resizemode # or "user" or "noresize"
          self.undobuffer = None
          TPen._reset(self)
  
      def _reset(self, pencolor=_CFG["pencolor"],
                       fillcolor=_CFG["fillcolor"]):
          self._pensize = 1
          self._shown = True
          self._pencolor = pencolor
          self._fillcolor = fillcolor
          self._drawing = True
          self._speed = 3
          self._stretchfactor = (1., 1.)
          self._shearfactor = 0.
          self._tilt = 0.
          self._shapetrafo = (1., 0., 0., 1.)
          self._outlinewidth = 1
  
      def resizemode(self, rmode=None):
          """Set resizemode to one of the values: "auto", "user", "noresize".
  
          (Optional) Argument:
          rmode -- one of the strings "auto", "user", "noresize"
  
          Different resizemodes have the following effects:
            - "auto" adapts the appearance of the turtle
                     corresponding to the value of pensize.
            - "user" adapts the appearance of the turtle according to the
                     values of stretchfactor and outlinewidth (outline),
                     which are set by shapesize()
            - "noresize" no adaption of the turtle's appearance takes place.
          If no argument is given, return current resizemode.
          resizemode("user") is called by a call of shapesize with arguments.
  
  
          Examples (for a Turtle instance named turtle):
          >>> turtle.resizemode("noresize")
          >>> turtle.resizemode()
          'noresize'
          """
          if rmode is None:
              return self._resizemode
          rmode = rmode.lower()
          if rmode in ["auto", "user", "noresize"]:
              self.pen(resizemode=rmode)
  
      def pensize(self, width=None):
          """Set or return the line thickness.
  
          Aliases:  pensize | width
  
          Argument:
          width -- positive number
  
          Set the line thickness to width or return it. If resizemode is set
          to "auto" and turtleshape is a polygon, that polygon is drawn with
          the same line thickness. If no argument is given, current pensize
          is returned.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.pensize()
          1
          >>> turtle.pensize(10)   # from here on lines of width 10 are drawn
          """
          if width is None:
              return self._pensize
          self.pen(pensize=width)
  
  
      def penup(self):
          """Pull the pen up -- no drawing when moving.
  
          Aliases: penup | pu | up
  
          No argument
  
          Example (for a Turtle instance named turtle):
          >>> turtle.penup()
          """
          if not self._drawing:
              return
          self.pen(pendown=False)
  
      def pendown(self):
          """Pull the pen down -- drawing when moving.
  
          Aliases: pendown | pd | down
  
          No argument.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.pendown()
          """
          if self._drawing:
              return
          self.pen(pendown=True)
  
      def isdown(self):
          """Return True if pen is down, False if it's up.
  
          No argument.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.penup()
          >>> turtle.isdown()
          False
          >>> turtle.pendown()
          >>> turtle.isdown()
          True
          """
          return self._drawing
  
      def speed(self, speed=None):
          """ Return or set the turtle's speed.
  
          Optional argument:
          speed -- an integer in the range 0..10 or a speedstring (see below)
  
          Set the turtle's speed to an integer value in the range 0 .. 10.
          If no argument is given: return current speed.
  
          If input is a number greater than 10 or smaller than 0.5,
          speed is set to 0.
          Speedstrings  are mapped to speedvalues in the following way:
              'fastest' :  0
              'fast'    :  10
              'normal'  :  6
              'slow'    :  3
              'slowest' :  1
          speeds from 1 to 10 enforce increasingly faster animation of
          line drawing and turtle turning.
  
          Attention:
          speed = 0 : *no* animation takes place. forward/back makes turtle jump
          and likewise left/right make the turtle turn instantly.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.speed(3)
          """
          speeds = {'fastest':0, 'fast':10, 'normal':6, 'slow':3, 'slowest':1 }
          if speed is None:
              return self._speed
          if speed in speeds:
              speed = speeds[speed]
          elif 0.5 < speed < 10.5:
              speed = int(round(speed))
          else:
              speed = 0
          self.pen(speed=speed)
  
      def color(self, *args):
          """Return or set the pencolor and fillcolor.
  
          Arguments:
          Several input formats are allowed.
          They use 0, 1, 2, or 3 arguments as follows:
  
          color()
              Return the current pencolor and the current fillcolor
              as a pair of color specification strings as are returned
              by pencolor and fillcolor.
          color(colorstring), color((r,g,b)), color(r,g,b)
              inputs as in pencolor, set both, fillcolor and pencolor,
              to the given value.
          color(colorstring1, colorstring2),
          color((r1,g1,b1), (r2,g2,b2))
              equivalent to pencolor(colorstring1) and fillcolor(colorstring2)
              and analogously, if the other input format is used.
  
          If turtleshape is a polygon, outline and interior of that polygon
          is drawn with the newly set colors.
          For more info see: pencolor, fillcolor
  
          Example (for a Turtle instance named turtle):
          >>> turtle.color('red', 'green')
          >>> turtle.color()
          ('red', 'green')
          >>> colormode(255)
          >>> color((40, 80, 120), (160, 200, 240))
          >>> color()
          ('#285078', '#a0c8f0')
          """
          if args:
              l = len(args)
              if l == 1:
                  pcolor = fcolor = args[0]
              elif l == 2:
                  pcolor, fcolor = args
              elif l == 3:
                  pcolor = fcolor = args
              pcolor = self._colorstr(pcolor)
              fcolor = self._colorstr(fcolor)
              self.pen(pencolor=pcolor, fillcolor=fcolor)
          else:
              return self._color(self._pencolor), self._color(self._fillcolor)
  
      def pencolor(self, *args):
          """ Return or set the pencolor.
  
          Arguments:
          Four input formats are allowed:
            - pencolor()
              Return the current pencolor as color specification string,
              possibly in hex-number format (see example).
              May be used as input to another color/pencolor/fillcolor call.
            - pencolor(colorstring)
              s is a Tk color specification string, such as "red" or "yellow"
            - pencolor((r, g, b))
              *a tuple* of r, g, and b, which represent, an RGB color,
              and each of r, g, and b are in the range 0..colormode,
              where colormode is either 1.0 or 255
            - pencolor(r, g, b)
              r, g, and b represent an RGB color, and each of r, g, and b
              are in the range 0..colormode
  
          If turtleshape is a polygon, the outline of that polygon is drawn
          with the newly set pencolor.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.pencolor('brown')
          >>> tup = (0.2, 0.8, 0.55)
          >>> turtle.pencolor(tup)
          >>> turtle.pencolor()
          '#33cc8c'
          """
          if args:
              color = self._colorstr(args)
              if color == self._pencolor:
                  return
              self.pen(pencolor=color)
          else:
              return self._color(self._pencolor)
  
      def fillcolor(self, *args):
          """ Return or set the fillcolor.
  
          Arguments:
          Four input formats are allowed:
            - fillcolor()
              Return the current fillcolor as color specification string,
              possibly in hex-number format (see example).
              May be used as input to another color/pencolor/fillcolor call.
            - fillcolor(colorstring)
              s is a Tk color specification string, such as "red" or "yellow"
            - fillcolor((r, g, b))
              *a tuple* of r, g, and b, which represent, an RGB color,
              and each of r, g, and b are in the range 0..colormode,
              where colormode is either 1.0 or 255
            - fillcolor(r, g, b)
              r, g, and b represent an RGB color, and each of r, g, and b
              are in the range 0..colormode
  
          If turtleshape is a polygon, the interior of that polygon is drawn
          with the newly set fillcolor.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.fillcolor('violet')
          >>> col = turtle.pencolor()
          >>> turtle.fillcolor(col)
          >>> turtle.fillcolor(0, .5, 0)
          """
          if args:
              color = self._colorstr(args)
              if color == self._fillcolor:
                  return
              self.pen(fillcolor=color)
          else:
              return self._color(self._fillcolor)
  
      def showturtle(self):
          """Makes the turtle visible.
  
          Aliases: showturtle | st
  
          No argument.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.hideturtle()
          >>> turtle.showturtle()
          """
          self.pen(shown=True)
  
      def hideturtle(self):
          """Makes the turtle invisible.
  
          Aliases: hideturtle | ht
  
          No argument.
  
          It's a good idea to do this while you're in the
          middle of a complicated drawing, because hiding
          the turtle speeds up the drawing observably.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.hideturtle()
          """
          self.pen(shown=False)
  
      def isvisible(self):
          """Return True if the Turtle is shown, False if it's hidden.
  
          No argument.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.hideturtle()
          >>> print turtle.isvisible():
          False
          """
          return self._shown
  
      def pen(self, pen=None, **pendict):
          """Return or set the pen's attributes.
  
          Arguments:
              pen -- a dictionary with some or all of the below listed keys.
              **pendict -- one or more keyword-arguments with the below
                           listed keys as keywords.
  
          Return or set the pen's attributes in a 'pen-dictionary'
          with the following key/value pairs:
             "shown"      :   True/False
             "pendown"    :   True/False
             "pencolor"   :   color-string or color-tuple
             "fillcolor"  :   color-string or color-tuple
             "pensize"    :   positive number
             "speed"      :   number in range 0..10
             "resizemode" :   "auto" or "user" or "noresize"
             "stretchfactor": (positive number, positive number)
             "shearfactor":   number
             "outline"    :   positive number
             "tilt"       :   number
  
          This dictionary can be used as argument for a subsequent
          pen()-call to restore the former pen-state. Moreover one
          or more of these attributes can be provided as keyword-arguments.
          This can be used to set several pen attributes in one statement.
  
  
          Examples (for a Turtle instance named turtle):
          >>> turtle.pen(fillcolor="black", pencolor="red", pensize=10)
          >>> turtle.pen()
          {'pensize': 10, 'shown': True, 'resizemode': 'auto', 'outline': 1,
          'pencolor': 'red', 'pendown': True, 'fillcolor': 'black',
          'stretchfactor': (1,1), 'speed': 3, 'shearfactor': 0.0}
          >>> penstate=turtle.pen()
          >>> turtle.color("yellow","")
          >>> turtle.penup()
          >>> turtle.pen()
          {'pensize': 10, 'shown': True, 'resizemode': 'auto', 'outline': 1,
          'pencolor': 'yellow', 'pendown': False, 'fillcolor': '',
          'stretchfactor': (1,1), 'speed': 3, 'shearfactor': 0.0}
          >>> p.pen(penstate, fillcolor="green")
          >>> p.pen()
          {'pensize': 10, 'shown': True, 'resizemode': 'auto', 'outline': 1,
          'pencolor': 'red', 'pendown': True, 'fillcolor': 'green',
          'stretchfactor': (1,1), 'speed': 3, 'shearfactor': 0.0}
          """
          _pd =  {"shown"         : self._shown,
                  "pendown"       : self._drawing,
                  "pencolor"      : self._pencolor,
                  "fillcolor"     : self._fillcolor,
                  "pensize"       : self._pensize,
                  "speed"         : self._speed,
                  "resizemode"    : self._resizemode,
                  "stretchfactor" : self._stretchfactor,
                  "shearfactor"   : self._shearfactor,
                  "outline"       : self._outlinewidth,
                  "tilt"          : self._tilt
                 }
  
          if not (pen or pendict):
              return _pd
  
          if isinstance(pen, dict):
              p = pen
          else:
              p = {}
          p.update(pendict)
  
          _p_buf = {}
          for key in p:
              _p_buf[key] = _pd[key]
  
          if self.undobuffer:
              self.undobuffer.push(("pen", _p_buf))
  
          newLine = False
          if "pendown" in p:
              if self._drawing != p["pendown"]:
                  newLine = True
          if "pencolor" in p:
              if isinstance(p["pencolor"], tuple):
                  p["pencolor"] = self._colorstr((p["pencolor"],))
              if self._pencolor != p["pencolor"]:
                  newLine = True
          if "pensize" in p:
              if self._pensize != p["pensize"]:
                  newLine = True
          if newLine:
              self._newLine()
          if "pendown" in p:
              self._drawing = p["pendown"]
          if "pencolor" in p:
              self._pencolor = p["pencolor"]
          if "pensize" in p:
              self._pensize = p["pensize"]
          if "fillcolor" in p:
              if isinstance(p["fillcolor"], tuple):
                  p["fillcolor"] = self._colorstr((p["fillcolor"],))
              self._fillcolor = p["fillcolor"]
          if "speed" in p:
              self._speed = p["speed"]
          if "resizemode" in p:
              self._resizemode = p["resizemode"]
          if "stretchfactor" in p:
              sf = p["stretchfactor"]
              if isinstance(sf, (int, float)):
                  sf = (sf, sf)
              self._stretchfactor = sf
          if "shearfactor" in p:
              self._shearfactor = p["shearfactor"]
          if "outline" in p:
              self._outlinewidth = p["outline"]
          if "shown" in p:
              self._shown = p["shown"]
          if "tilt" in p:
              self._tilt = p["tilt"]
          if "stretchfactor" in p or "tilt" in p or "shearfactor" in p:
              scx, scy = self._stretchfactor
              shf = self._shearfactor
              sa, ca = math.sin(self._tilt), math.cos(self._tilt)
              self._shapetrafo = ( scx*ca, scy*(shf*ca + sa),
                                  -scx*sa, scy*(ca - shf*sa))
          self._update()
  
  ## three dummy methods to be implemented by child class:
  
      def _newLine(self, usePos = True):
          """dummy method - to be overwritten by child class"""
      def _update(self, count=True, forced=False):
          """dummy method - to be overwritten by child class"""
      def _color(self, args):
          """dummy method - to be overwritten by child class"""
      def _colorstr(self, args):
          """dummy method - to be overwritten by child class"""
  
      width = pensize
      up = penup
      pu = penup
      pd = pendown
      down = pendown
      st = showturtle
      ht = hideturtle
  
  
  class _TurtleImage(object):
      """Helper class: Datatype to store Turtle attributes
      """
  
      def __init__(self, screen, shapeIndex):
          self.screen = screen
          self._type = None
          self._setshape(shapeIndex)
  
      def _setshape(self, shapeIndex):
          screen = self.screen
          self.shapeIndex = shapeIndex
          if self._type == "polygon" == screen._shapes[shapeIndex]._type:
              return
          if self._type == "image" == screen._shapes[shapeIndex]._type:
              return
          if self._type in ["image", "polygon"]:
              screen._delete(self._item)
          elif self._type == "compound":
              for item in self._item:
                  screen._delete(item)
          self._type = screen._shapes[shapeIndex]._type
          if self._type == "polygon":
              self._item = screen._createpoly()
          elif self._type == "image":
              self._item = screen._createimage(screen._shapes["blank"]._data)
          elif self._type == "compound":
              self._item = [screen._createpoly() for item in
                                            screen._shapes[shapeIndex]._data]
  
  
  class RawTurtle(TPen, TNavigator):
      """Animation part of the RawTurtle.
      Puts RawTurtle upon a TurtleScreen and provides tools for
      its animation.
      """
      screens = []
  
      def __init__(self, canvas=None,
                   shape=_CFG["shape"],
                   undobuffersize=_CFG["undobuffersize"],
                   visible=_CFG["visible"]):
          if isinstance(canvas, _Screen):
              self.screen = canvas
          elif isinstance(canvas, TurtleScreen):
              if canvas not in RawTurtle.screens:
                  RawTurtle.screens.append(canvas)
              self.screen = canvas
          elif isinstance(canvas, (ScrolledCanvas, Canvas)):
              for screen in RawTurtle.screens:
                  if screen.cv == canvas:
                      self.screen = screen
                      break
              else:
                  self.screen = TurtleScreen(canvas)
                  RawTurtle.screens.append(self.screen)
          else:
              raise TurtleGraphicsError("bad canvas argument %s" % canvas)
  
          screen = self.screen
          TNavigator.__init__(self, screen.mode())
          TPen.__init__(self)
          screen._turtles.append(self)
          self.drawingLineItem = screen._createline()
          self.turtle = _TurtleImage(screen, shape)
          self._poly = None
          self._creatingPoly = False
          self._fillitem = self._fillpath = None
          self._shown = visible
          self._hidden_from_screen = False
          self.currentLineItem = screen._createline()
          self.currentLine = [self._position]
          self.items = [self.currentLineItem]
          self.stampItems = []
          self._undobuffersize = undobuffersize
          self.undobuffer = Tbuffer(undobuffersize)
          self._update()
  
      def reset(self):
          """Delete the turtle's drawings and restore its default values.
  
          No argument.
  
          Delete the turtle's drawings from the screen, re-center the turtle
          and set variables to the default values.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.position()
          (0.00,-22.00)
          >>> turtle.heading()
          100.0
          >>> turtle.reset()
          >>> turtle.position()
          (0.00,0.00)
          >>> turtle.heading()
          0.0
          """
          TNavigator.reset(self)
          TPen._reset(self)
          self._clear()
          self._drawturtle()
          self._update()
  
      def setundobuffer(self, size):
          """Set or disable undobuffer.
  
          Argument:
          size -- an integer or None
  
          If size is an integer an empty undobuffer of given size is installed.
          Size gives the maximum number of turtle-actions that can be undone
          by the undo() function.
          If size is None, no undobuffer is present.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.setundobuffer(42)
          """
          if size is None or size <= 0:
              self.undobuffer = None
          else:
              self.undobuffer = Tbuffer(size)
  
      def undobufferentries(self):
          """Return count of entries in the undobuffer.
  
          No argument.
  
          Example (for a Turtle instance named turtle):
          >>> while undobufferentries():
          ...     undo()
          """
          if self.undobuffer is None:
              return 0
          return self.undobuffer.nr_of_items()
  
      def _clear(self):
          """Delete all of pen's drawings"""
          self._fillitem = self._fillpath = None
          for item in self.items:
              self.screen._delete(item)
          self.currentLineItem = self.screen._createline()
          self.currentLine = []
          if self._drawing:
              self.currentLine.append(self._position)
          self.items = [self.currentLineItem]
          self.clearstamps()
          self.setundobuffer(self._undobuffersize)
  
  
      def clear(self):
          """Delete the turtle's drawings from the screen. Do not move turtle.
  
          No arguments.
  
          Delete the turtle's drawings from the screen. Do not move turtle.
          State and position of the turtle as well as drawings of other
          turtles are not affected.
  
          Examples (for a Turtle instance named turtle):
          >>> turtle.clear()
          """
          self._clear()
          self._update()
  
      def _update_data(self):
          self.screen._incrementudc()
          if self.screen._updatecounter != 0:
              return
          if len(self.currentLine)>1:
              self.screen._drawline(self.currentLineItem, self.currentLine,
                                    self._pencolor, self._pensize)
  
      def _update(self):
          """Perform a Turtle-data update.
          """
          screen = self.screen
          if screen._tracing == 0:
              return
          elif screen._tracing == 1:
              self._update_data()
              self._drawturtle()
              screen._update()                  # TurtleScreenBase
              screen._delay(screen._delayvalue) # TurtleScreenBase
          else:
              self._update_data()
              if screen._updatecounter == 0:
                  for t in screen.turtles():
                      t._drawturtle()
                  screen._update()
  
      def _tracer(self, flag=None, delay=None):
          """Turns turtle animation on/off and set delay for update drawings.
  
          Optional arguments:
          n -- nonnegative  integer
          delay -- nonnegative  integer
  
          If n is given, only each n-th regular screen update is really performed.
          (Can be used to accelerate the drawing of complex graphics.)
          Second arguments sets delay value (see RawTurtle.delay())
  
          Example (for a Turtle instance named turtle):
          >>> turtle.tracer(8, 25)
          >>> dist = 2
          >>> for i in range(200):
          ...     turtle.fd(dist)
          ...     turtle.rt(90)
          ...     dist += 2
          """
          return self.screen.tracer(flag, delay)
  
      def _color(self, args):
          return self.screen._color(args)
  
      def _colorstr(self, args):
          return self.screen._colorstr(args)
  
      def _cc(self, args):
          """Convert colortriples to hexstrings.
          """
          if isinstance(args, str):
              return args
          try:
              r, g, b = args
          except (TypeError, ValueError):
              raise TurtleGraphicsError("bad color arguments: %s" % str(args))
          if self.screen._colormode == 1.0:
              r, g, b = [round(255.0*x) for x in (r, g, b)]
          if not ((0 <= r <= 255) and (0 <= g <= 255) and (0 <= b <= 255)):
              raise TurtleGraphicsError("bad color sequence: %s" % str(args))
          return "#%02x%02x%02x" % (r, g, b)
  
      def clone(self):
          """Create and return a clone of the turtle.
  
          No argument.
  
          Create and return a clone of the turtle with same position, heading
          and turtle properties.
  
          Example (for a Turtle instance named mick):
          mick = Turtle()
          joe = mick.clone()
          """
          screen = self.screen
          self._newLine(self._drawing)
  
          turtle = self.turtle
          self.screen = None
          self.turtle = None  # too make self deepcopy-able
  
          q = deepcopy(self)
  
          self.screen = screen
          self.turtle = turtle
  
          q.screen = screen
          q.turtle = _TurtleImage(screen, self.turtle.shapeIndex)
  
          screen._turtles.append(q)
          ttype = screen._shapes[self.turtle.shapeIndex]._type
          if ttype == "polygon":
              q.turtle._item = screen._createpoly()
          elif ttype == "image":
              q.turtle._item = screen._createimage(screen._shapes["blank"]._data)
          elif ttype == "compound":
              q.turtle._item = [screen._createpoly() for item in
                                screen._shapes[self.turtle.shapeIndex]._data]
          q.currentLineItem = screen._createline()
          q._update()
          return q
  
      def shape(self, name=None):
          """Set turtle shape to shape with given name / return current shapename.
  
          Optional argument:
          name -- a string, which is a valid shapename
  
          Set turtle shape to shape with given name or, if name is not given,
          return name of current shape.
          Shape with name must exist in the TurtleScreen's shape dictionary.
          Initially there are the following polygon shapes:
          'arrow', 'turtle', 'circle', 'square', 'triangle', 'classic'.
          To learn about how to deal with shapes see Screen-method register_shape.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.shape()
          'arrow'
          >>> turtle.shape("turtle")
          >>> turtle.shape()
          'turtle'
          """
          if name is None:
              return self.turtle.shapeIndex
          if not name in self.screen.getshapes():
              raise TurtleGraphicsError("There is no shape named %s" % name)
          self.turtle._setshape(name)
          self._update()
  
      def shapesize(self, stretch_wid=None, stretch_len=None, outline=None):
          """Set/return turtle's stretchfactors/outline. Set resizemode to "user".
  
          Optional arguments:
             stretch_wid : positive number
             stretch_len : positive number
             outline  : positive number
  
          Return or set the pen's attributes x/y-stretchfactors and/or outline.
          Set resizemode to "user".
          If and only if resizemode is set to "user", the turtle will be displayed
          stretched according to its stretchfactors:
          stretch_wid is stretchfactor perpendicular to orientation
          stretch_len is stretchfactor in direction of turtles orientation.
          outline determines the width of the shapes's outline.
  
          Examples (for a Turtle instance named turtle):
          >>> turtle.resizemode("user")
          >>> turtle.shapesize(5, 5, 12)
          >>> turtle.shapesize(outline=8)
          """
          if stretch_wid is stretch_len is outline is None:
              stretch_wid, stretch_len = self._stretchfactor
              return stretch_wid, stretch_len, self._outlinewidth
          if stretch_wid == 0 or stretch_len == 0:
              raise TurtleGraphicsError("stretch_wid/stretch_len must not be zero")
          if stretch_wid is not None:
              if stretch_len is None:
                  stretchfactor = stretch_wid, stretch_wid
              else:
                  stretchfactor = stretch_wid, stretch_len
          elif stretch_len is not None:
              stretchfactor = self._stretchfactor[0], stretch_len
          else:
              stretchfactor = self._stretchfactor
          if outline is None:
              outline = self._outlinewidth
          self.pen(resizemode="user",
                   stretchfactor=stretchfactor, outline=outline)
  
      def shearfactor(self, shear=None):
          """Set or return the current shearfactor.
  
          Optional argument: shear -- number, tangent of the shear angle
  
          Shear the turtleshape according to the given shearfactor shear,
          which is the tangent of the shear angle. DO NOT change the
          turtle's heading (direction of movement).
          If shear is not given: return the current shearfactor, i. e. the
          tangent of the shear angle, by which lines parallel to the
          heading of the turtle are sheared.
  
          Examples (for a Turtle instance named turtle):
          >>> turtle.shape("circle")
          >>> turtle.shapesize(5,2)
          >>> turtle.shearfactor(0.5)
          >>> turtle.shearfactor()
          >>> 0.5
          """
          if shear is None:
              return self._shearfactor
          self.pen(resizemode="user", shearfactor=shear)
  
      def settiltangle(self, angle):
          """Rotate the turtleshape to point in the specified direction
  
          Argument: angle -- number
  
          Rotate the turtleshape to point in the direction specified by angle,
          regardless of its current tilt-angle. DO NOT change the turtle's
          heading (direction of movement).
  
  
          Examples (for a Turtle instance named turtle):
          >>> turtle.shape("circle")
          >>> turtle.shapesize(5,2)
          >>> turtle.settiltangle(45)
          >>> stamp()
          >>> turtle.fd(50)
          >>> turtle.settiltangle(-45)
          >>> stamp()
          >>> turtle.fd(50)
          """
          tilt = -angle * self._degreesPerAU * self._angleOrient
          tilt = (tilt * math.pi / 180.0) % (2*math.pi)
          self.pen(resizemode="user", tilt=tilt)
  
      def tiltangle(self, angle=None):
          """Set or return the current tilt-angle.
  
          Optional argument: angle -- number
  
          Rotate the turtleshape to point in the direction specified by angle,
          regardless of its current tilt-angle. DO NOT change the turtle's
          heading (direction of movement).
          If angle is not given: return the current tilt-angle, i. e. the angle
          between the orientation of the turtleshape and the heading of the
          turtle (its direction of movement).
  
          Deprecated since Python 3.1
  
          Examples (for a Turtle instance named turtle):
          >>> turtle.shape("circle")
          >>> turtle.shapesize(5,2)
          >>> turtle.tilt(45)
          >>> turtle.tiltangle()
          """
          if angle is None:
              tilt = -self._tilt * (180.0/math.pi) * self._angleOrient
              return (tilt / self._degreesPerAU) % self._fullcircle
          else:
              self.settiltangle(angle)
  
      def tilt(self, angle):
          """Rotate the turtleshape by angle.
  
          Argument:
          angle - a number
  
          Rotate the turtleshape by angle from its current tilt-angle,
          but do NOT change the turtle's heading (direction of movement).
  
          Examples (for a Turtle instance named turtle):
          >>> turtle.shape("circle")
          >>> turtle.shapesize(5,2)
          >>> turtle.tilt(30)
          >>> turtle.fd(50)
          >>> turtle.tilt(30)
          >>> turtle.fd(50)
          """
          self.settiltangle(angle + self.tiltangle())
  
      def shapetransform(self, t11=None, t12=None, t21=None, t22=None):
          """Set or return the current transformation matrix of the turtle shape.
  
          Optional arguments: t11, t12, t21, t22 -- numbers.
  
          If none of the matrix elements are given, return the transformation
          matrix.
          Otherwise set the given elements and transform the turtleshape
          according to the matrix consisting of first row t11, t12 and
          second row t21, 22.
          Modify stretchfactor, shearfactor and tiltangle according to the
          given matrix.
  
          Examples (for a Turtle instance named turtle):
          >>> turtle.shape("square")
          >>> turtle.shapesize(4,2)
          >>> turtle.shearfactor(-0.5)
          >>> turtle.shapetransform()
          (4.0, -1.0, -0.0, 2.0)
          """
          if t11 is t12 is t21 is t22 is None:
              return self._shapetrafo
          m11, m12, m21, m22 = self._shapetrafo
          if t11 is not None: m11 = t11
          if t12 is not None: m12 = t12
          if t21 is not None: m21 = t21
          if t22 is not None: m22 = t22
          if t11 * t22 - t12 * t21 == 0:
              raise TurtleGraphicsError("Bad shape transform matrix: must not be singular")
          self._shapetrafo = (m11, m12, m21, m22)
          alfa = math.atan2(-m21, m11) % (2 * math.pi)
          sa, ca = math.sin(alfa), math.cos(alfa)
          a11, a12, a21, a22 = (ca*m11 - sa*m21, ca*m12 - sa*m22,
                                sa*m11 + ca*m21, sa*m12 + ca*m22)
          self._stretchfactor = a11, a22
          self._shearfactor = a12/a22
          self._tilt = alfa
          self.pen(resizemode="user")
  
  
      def _polytrafo(self, poly):
          """Computes transformed polygon shapes from a shape
          according to current position and heading.
          """
          screen = self.screen
          p0, p1 = self._position
          e0, e1 = self._orient
          e = Vec2D(e0, e1 * screen.yscale / screen.xscale)
          e0, e1 = (1.0 / abs(e)) * e
          return [(p0+(e1*x+e0*y)/screen.xscale, p1+(-e0*x+e1*y)/screen.yscale)
                                                             for (x, y) in poly]
  
      def get_shapepoly(self):
          """Return the current shape polygon as tuple of coordinate pairs.
  
          No argument.
  
          Examples (for a Turtle instance named turtle):
          >>> turtle.shape("square")
          >>> turtle.shapetransform(4, -1, 0, 2)
          >>> turtle.get_shapepoly()
          ((50, -20), (30, 20), (-50, 20), (-30, -20))
  
          """
          shape = self.screen._shapes[self.turtle.shapeIndex]
          if shape._type == "polygon":
              return self._getshapepoly(shape._data, shape._type == "compound")
          # else return None
  
      def _getshapepoly(self, polygon, compound=False):
          """Calculate transformed shape polygon according to resizemode
          and shapetransform.
          """
          if self._resizemode == "user" or compound:
              t11, t12, t21, t22 = self._shapetrafo
          elif self._resizemode == "auto":
              l = max(1, self._pensize/5.0)
              t11, t12, t21, t22 = l, 0, 0, l
          elif self._resizemode == "noresize":
              return polygon
          return tuple((t11*x + t12*y, t21*x + t22*y) for (x, y) in polygon)
  
      def _drawturtle(self):
          """Manages the correct rendering of the turtle with respect to
          its shape, resizemode, stretch and tilt etc."""
          screen = self.screen
          shape = screen._shapes[self.turtle.shapeIndex]
          ttype = shape._type
          titem = self.turtle._item
          if self._shown and screen._updatecounter == 0 and screen._tracing > 0:
              self._hidden_from_screen = False
              tshape = shape._data
              if ttype == "polygon":
                  if self._resizemode == "noresize": w = 1
                  elif self._resizemode == "auto": w = self._pensize
                  else: w =self._outlinewidth
                  shape = self._polytrafo(self._getshapepoly(tshape))
                  fc, oc = self._fillcolor, self._pencolor
                  screen._drawpoly(titem, shape, fill=fc, outline=oc,
                                                        width=w, top=True)
              elif ttype == "image":
                  screen._drawimage(titem, self._position, tshape)
              elif ttype == "compound":
                  for item, (poly, fc, oc) in zip(titem, tshape):
                      poly = self._polytrafo(self._getshapepoly(poly, True))
                      screen._drawpoly(item, poly, fill=self._cc(fc),
                                       outline=self._cc(oc), width=self._outlinewidth, top=True)
          else:
              if self._hidden_from_screen:
                  return
              if ttype == "polygon":
                  screen._drawpoly(titem, ((0, 0), (0, 0), (0, 0)), "", "")
              elif ttype == "image":
                  screen._drawimage(titem, self._position,
                                            screen._shapes["blank"]._data)
              elif ttype == "compound":
                  for item in titem:
                      screen._drawpoly(item, ((0, 0), (0, 0), (0, 0)), "", "")
              self._hidden_from_screen = True
  
  ##############################  stamp stuff  ###############################
  
      def stamp(self):
          """Stamp a copy of the turtleshape onto the canvas and return its id.
  
          No argument.
  
          Stamp a copy of the turtle shape onto the canvas at the current
          turtle position. Return a stamp_id for that stamp, which can be
          used to delete it by calling clearstamp(stamp_id).
  
          Example (for a Turtle instance named turtle):
          >>> turtle.color("blue")
          >>> turtle.stamp()
          13
          >>> turtle.fd(50)
          """
          screen = self.screen
          shape = screen._shapes[self.turtle.shapeIndex]
          ttype = shape._type
          tshape = shape._data
          if ttype == "polygon":
              stitem = screen._createpoly()
              if self._resizemode == "noresize": w = 1
              elif self._resizemode == "auto": w = self._pensize
              else: w =self._outlinewidth
              shape = self._polytrafo(self._getshapepoly(tshape))
              fc, oc = self._fillcolor, self._pencolor
              screen._drawpoly(stitem, shape, fill=fc, outline=oc,
                                                    width=w, top=True)
          elif ttype == "image":
              stitem = screen._createimage("")
              screen._drawimage(stitem, self._position, tshape)
          elif ttype == "compound":
              stitem = []
              for element in tshape:
                  item = screen._createpoly()
                  stitem.append(item)
              stitem = tuple(stitem)
              for item, (poly, fc, oc) in zip(stitem, tshape):
                  poly = self._polytrafo(self._getshapepoly(poly, True))
                  screen._drawpoly(item, poly, fill=self._cc(fc),
                                   outline=self._cc(oc), width=self._outlinewidth, top=True)
          self.stampItems.append(stitem)
          self.undobuffer.push(("stamp", stitem))
          return stitem
  
      def _clearstamp(self, stampid):
          """does the work for clearstamp() and clearstamps()
          """
          if stampid in self.stampItems:
              if isinstance(stampid, tuple):
                  for subitem in stampid:
                      self.screen._delete(subitem)
              else:
                  self.screen._delete(stampid)
              self.stampItems.remove(stampid)
          # Delete stampitem from undobuffer if necessary
          # if clearstamp is called directly.
          item = ("stamp", stampid)
          buf = self.undobuffer
          if item not in buf.buffer:
              return
          index = buf.buffer.index(item)
          buf.buffer.remove(item)
          if index <= buf.ptr:
              buf.ptr = (buf.ptr - 1) % buf.bufsize
          buf.buffer.insert((buf.ptr+1)%buf.bufsize, [None])
  
      def clearstamp(self, stampid):
          """Delete stamp with given stampid
  
          Argument:
          stampid - an integer, must be return value of previous stamp() call.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.color("blue")
          >>> astamp = turtle.stamp()
          >>> turtle.fd(50)
          >>> turtle.clearstamp(astamp)
          """
          self._clearstamp(stampid)
          self._update()
  
      def clearstamps(self, n=None):
          """Delete all or first/last n of turtle's stamps.
  
          Optional argument:
          n -- an integer
  
          If n is None, delete all of pen's stamps,
          else if n > 0 delete first n stamps
          else if n < 0 delete last n stamps.
  
          Example (for a Turtle instance named turtle):
          >>> for i in range(8):
          ...     turtle.stamp(); turtle.fd(30)
          ...
          >>> turtle.clearstamps(2)
          >>> turtle.clearstamps(-2)
          >>> turtle.clearstamps()
          """
          if n is None:
              toDelete = self.stampItems[:]
          elif n >= 0:
              toDelete = self.stampItems[:n]
          else:
              toDelete = self.stampItems[n:]
          for item in toDelete:
              self._clearstamp(item)
          self._update()
  
      def _goto(self, end):
          """Move the pen to the point end, thereby drawing a line
          if pen is down. All other methods for turtle movement depend
          on this one.
          """
          ## Version with undo-stuff
          go_modes = ( self._drawing,
                       self._pencolor,
                       self._pensize,
                       isinstance(self._fillpath, list))
          screen = self.screen
          undo_entry = ("go", self._position, end, go_modes,
                        (self.currentLineItem,
                        self.currentLine[:],
                        screen._pointlist(self.currentLineItem),
                        self.items[:])
                        )
          if self.undobuffer:
              self.undobuffer.push(undo_entry)
          start = self._position
          if self._speed and screen._tracing == 1:
              diff = (end-start)
              diffsq = (diff[0]*screen.xscale)**2 + (diff[1]*screen.yscale)**2
              nhops = 1+int((diffsq**0.5)/(3*(1.1**self._speed)*self._speed))
              delta = diff * (1.0/nhops)
              for n in range(1, nhops):
                  if n == 1:
                      top = True
                  else:
                      top = False
                  self._position = start + delta * n
                  if self._drawing:
                      screen._drawline(self.drawingLineItem,
                                       (start, self._position),
                                       self._pencolor, self._pensize, top)
                  self._update()
              if self._drawing:
                  screen._drawline(self.drawingLineItem, ((0, 0), (0, 0)),
                                                 fill="", width=self._pensize)
          # Turtle now at end,
          if self._drawing: # now update currentLine
              self.currentLine.append(end)
          if isinstance(self._fillpath, list):
              self._fillpath.append(end)
          ######    vererbung!!!!!!!!!!!!!!!!!!!!!!
          self._position = end
          if self._creatingPoly:
              self._poly.append(end)
          if len(self.currentLine) > 42: # 42! answer to the ultimate question
                                         # of life, the universe and everything
              self._newLine()
          self._update() #count=True)
  
      def _undogoto(self, entry):
          """Reverse a _goto. Used for undo()
          """
          old, new, go_modes, coodata = entry
          drawing, pc, ps, filling = go_modes
          cLI, cL, pl, items = coodata
          screen = self.screen
          if abs(self._position - new) > 0.5:
              print ("undogoto: HALLO-DA-STIMMT-WAS-NICHT!")
          # restore former situation
          self.currentLineItem = cLI
          self.currentLine = cL
  
          if pl == [(0, 0), (0, 0)]:
              usepc = ""
          else:
              usepc = pc
          screen._drawline(cLI, pl, fill=usepc, width=ps)
  
          todelete = [i for i in self.items if (i not in items) and
                                         (screen._type(i) == "line")]
          for i in todelete:
              screen._delete(i)
              self.items.remove(i)
  
          start = old
          if self._speed and screen._tracing == 1:
              diff = old - new
              diffsq = (diff[0]*screen.xscale)**2 + (diff[1]*screen.yscale)**2
              nhops = 1+int((diffsq**0.5)/(3*(1.1**self._speed)*self._speed))
              delta = diff * (1.0/nhops)
              for n in range(1, nhops):
                  if n == 1:
                      top = True
                  else:
                      top = False
                  self._position = new + delta * n
                  if drawing:
                      screen._drawline(self.drawingLineItem,
                                       (start, self._position),
                                       pc, ps, top)
                  self._update()
              if drawing:
                  screen._drawline(self.drawingLineItem, ((0, 0), (0, 0)),
                                                 fill="", width=ps)
          # Turtle now at position old,
          self._position = old
          ##  if undo is done during creating a polygon, the last vertex
          ##  will be deleted. if the polygon is entirely deleted,
          ##  creatingPoly will be set to False.
          ##  Polygons created before the last one will not be affected by undo()
          if self._creatingPoly:
              if len(self._poly) > 0:
                  self._poly.pop()
              if self._poly == []:
                  self._creatingPoly = False
                  self._poly = None
          if filling:
              if self._fillpath == []:
                  self._fillpath = None
                  print("Unwahrscheinlich in _undogoto!")
              elif self._fillpath is not None:
                  self._fillpath.pop()
          self._update() #count=True)
  
      def _rotate(self, angle):
          """Turns pen clockwise by angle.
          """
          if self.undobuffer:
              self.undobuffer.push(("rot", angle, self._degreesPerAU))
          angle *= self._degreesPerAU
          neworient = self._orient.rotate(angle)
          tracing = self.screen._tracing
          if tracing == 1 and self._speed > 0:
              anglevel = 3.0 * self._speed
              steps = 1 + int(abs(angle)/anglevel)
              delta = 1.0*angle/steps
              for _ in range(steps):
                  self._orient = self._orient.rotate(delta)
                  self._update()
          self._orient = neworient
          self._update()
  
      def _newLine(self, usePos=True):
          """Closes current line item and starts a new one.
             Remark: if current line became too long, animation
             performance (via _drawline) slowed down considerably.
          """
          if len(self.currentLine) > 1:
              self.screen._drawline(self.currentLineItem, self.currentLine,
                                        self._pencolor, self._pensize)
              self.currentLineItem = self.screen._createline()
              self.items.append(self.currentLineItem)
          else:
              self.screen._drawline(self.currentLineItem, top=True)
          self.currentLine = []
          if usePos:
              self.currentLine = [self._position]
  
      def filling(self):
          """Return fillstate (True if filling, False else).
  
          No argument.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.begin_fill()
          >>> if turtle.filling():
          ...     turtle.pensize(5)
          ... else:
          ...     turtle.pensize(3)
          """
          return isinstance(self._fillpath, list)
  
      def begin_fill(self):
          """Called just before drawing a shape to be filled.
  
          No argument.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.color("black", "red")
          >>> turtle.begin_fill()
          >>> turtle.circle(60)
          >>> turtle.end_fill()
          """
          if not self.filling():
              self._fillitem = self.screen._createpoly()
              self.items.append(self._fillitem)
          self._fillpath = [self._position]
          self._newLine()
          if self.undobuffer:
              self.undobuffer.push(("beginfill", self._fillitem))
          self._update()
  
  
      def end_fill(self):
          """Fill the shape drawn after the call begin_fill().
  
          No argument.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.color("black", "red")
          >>> turtle.begin_fill()
          >>> turtle.circle(60)
          >>> turtle.end_fill()
          """
          if self.filling():
              if len(self._fillpath) > 2:
                  self.screen._drawpoly(self._fillitem, self._fillpath,
                                        fill=self._fillcolor)
                  if self.undobuffer:
                      self.undobuffer.push(("dofill", self._fillitem))
              self._fillitem = self._fillpath = None
              self._update()
  
      def dot(self, size=None, *color):
          """Draw a dot with diameter size, using color.
  
          Optional arguments:
          size -- an integer >= 1 (if given)
          color -- a colorstring or a numeric color tuple
  
          Draw a circular dot with diameter size, using color.
          If size is not given, the maximum of pensize+4 and 2*pensize is used.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.dot()
          >>> turtle.fd(50); turtle.dot(20, "blue"); turtle.fd(50)
          """
          if not color:
              if isinstance(size, (str, tuple)):
                  color = self._colorstr(size)
                  size = self._pensize + max(self._pensize, 4)
              else:
                  color = self._pencolor
                  if not size:
                      size = self._pensize + max(self._pensize, 4)
          else:
              if size is None:
                  size = self._pensize + max(self._pensize, 4)
              color = self._colorstr(color)
          if hasattr(self.screen, "_dot"):
              item = self.screen._dot(self._position, size, color)
              self.items.append(item)
              if self.undobuffer:
                  self.undobuffer.push(("dot", item))
          else:
              pen = self.pen()
              if self.undobuffer:
                  self.undobuffer.push(["seq"])
                  self.undobuffer.cumulate = True
              try:
                  if self.resizemode() == 'auto':
                      self.ht()
                  self.pendown()
                  self.pensize(size)
                  self.pencolor(color)
                  self.forward(0)
              finally:
                  self.pen(pen)
              if self.undobuffer:
                  self.undobuffer.cumulate = False
  
      def _write(self, txt, align, font):
          """Performs the writing for write()
          """
          item, end = self.screen._write(self._position, txt, align, font,
                                                            self._pencolor)
          self.items.append(item)
          if self.undobuffer:
              self.undobuffer.push(("wri", item))
          return end
  
      def write(self, arg, move=False, align="left", font=("Arial", 8, "normal")):
          """Write text at the current turtle position.
  
          Arguments:
          arg -- info, which is to be written to the TurtleScreen
          move (optional) -- True/False
          align (optional) -- one of the strings "left", "center" or right"
          font (optional) -- a triple (fontname, fontsize, fonttype)
  
          Write text - the string representation of arg - at the current
          turtle position according to align ("left", "center" or right")
          and with the given font.
          If move is True, the pen is moved to the bottom-right corner
          of the text. By default, move is False.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.write('Home = ', True, align="center")
          >>> turtle.write((0,0), True)
          """
          if self.undobuffer:
              self.undobuffer.push(["seq"])
              self.undobuffer.cumulate = True
          end = self._write(str(arg), align.lower(), font)
          if move:
              x, y = self.pos()
              self.setpos(end, y)
          if self.undobuffer:
              self.undobuffer.cumulate = False
  
      def begin_poly(self):
          """Start recording the vertices of a polygon.
  
          No argument.
  
          Start recording the vertices of a polygon. Current turtle position
          is first point of polygon.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.begin_poly()
          """
          self._poly = [self._position]
          self._creatingPoly = True
  
      def end_poly(self):
          """Stop recording the vertices of a polygon.
  
          No argument.
  
          Stop recording the vertices of a polygon. Current turtle position is
          last point of polygon. This will be connected with the first point.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.end_poly()
          """
          self._creatingPoly = False
  
      def get_poly(self):
          """Return the lastly recorded polygon.
  
          No argument.
  
          Example (for a Turtle instance named turtle):
          >>> p = turtle.get_poly()
          >>> turtle.register_shape("myFavouriteShape", p)
          """
          ## check if there is any poly?
          if self._poly is not None:
              return tuple(self._poly)
  
      def getscreen(self):
          """Return the TurtleScreen object, the turtle is drawing  on.
  
          No argument.
  
          Return the TurtleScreen object, the turtle is drawing  on.
          So TurtleScreen-methods can be called for that object.
  
          Example (for a Turtle instance named turtle):
          >>> ts = turtle.getscreen()
          >>> ts
          <turtle.TurtleScreen object at 0x0106B770>
          >>> ts.bgcolor("pink")
          """
          return self.screen
  
      def getturtle(self):
          """Return the Turtleobject itself.
  
          No argument.
  
          Only reasonable use: as a function to return the 'anonymous turtle':
  
          Example:
          >>> pet = getturtle()
          >>> pet.fd(50)
          >>> pet
          <turtle.Turtle object at 0x0187D810>
          >>> turtles()
          [<turtle.Turtle object at 0x0187D810>]
          """
          return self
  
      getpen = getturtle
  
  
      ################################################################
      ### screen oriented methods recurring to methods of TurtleScreen
      ################################################################
  
      def _delay(self, delay=None):
          """Set delay value which determines speed of turtle animation.
          """
          return self.screen.delay(delay)
  
      def onclick(self, fun, btn=1, add=None):
          """Bind fun to mouse-click event on this turtle on canvas.
  
          Arguments:
          fun --  a function with two arguments, to which will be assigned
                  the coordinates of the clicked point on the canvas.
          btn --  number of the mouse-button defaults to 1 (left mouse button).
          add --  True or False. If True, new binding will be added, otherwise
                  it will replace a former binding.
  
          Example for the anonymous turtle, i. e. the procedural way:
  
          >>> def turn(x, y):
          ...     left(360)
          ...
          >>> onclick(turn)  # Now clicking into the turtle will turn it.
          >>> onclick(None)  # event-binding will be removed
          """
          self.screen._onclick(self.turtle._item, fun, btn, add)
          self._update()
  
      def onrelease(self, fun, btn=1, add=None):
          """Bind fun to mouse-button-release event on this turtle on canvas.
  
          Arguments:
          fun -- a function with two arguments, to which will be assigned
                  the coordinates of the clicked point on the canvas.
          btn --  number of the mouse-button defaults to 1 (left mouse button).
  
          Example (for a MyTurtle instance named joe):
          >>> class MyTurtle(Turtle):
          ...     def glow(self,x,y):
          ...             self.fillcolor("red")
          ...     def unglow(self,x,y):
          ...             self.fillcolor("")
          ...
          >>> joe = MyTurtle()
          >>> joe.onclick(joe.glow)
          >>> joe.onrelease(joe.unglow)
  
          Clicking on joe turns fillcolor red, unclicking turns it to
          transparent.
          """
          self.screen._onrelease(self.turtle._item, fun, btn, add)
          self._update()
  
      def ondrag(self, fun, btn=1, add=None):
          """Bind fun to mouse-move event on this turtle on canvas.
  
          Arguments:
          fun -- a function with two arguments, to which will be assigned
                 the coordinates of the clicked point on the canvas.
          btn -- number of the mouse-button defaults to 1 (left mouse button).
  
          Every sequence of mouse-move-events on a turtle is preceded by a
          mouse-click event on that turtle.
  
          Example (for a Turtle instance named turtle):
          >>> turtle.ondrag(turtle.goto)
  
          Subsequently clicking and dragging a Turtle will move it
          across the screen thereby producing handdrawings (if pen is
          down).
          """
          self.screen._ondrag(self.turtle._item, fun, btn, add)
  
  
      def _undo(self, action, data):
          """Does the main part of the work for undo()
          """
          if self.undobuffer is None:
              return
          if action == "rot":
              angle, degPAU = data
              self._rotate(-angle*degPAU/self._degreesPerAU)
              dummy = self.undobuffer.pop()
          elif action == "stamp":
              stitem = data[0]
              self.clearstamp(stitem)
          elif action == "go":
              self._undogoto(data)
          elif action in ["wri", "dot"]:
              item = data[0]
              self.screen._delete(item)
              self.items.remove(item)
          elif action == "dofill":
              item = data[0]
              self.screen._drawpoly(item, ((0, 0),(0, 0),(0, 0)),
                                    fill="", outline="")
          elif action == "beginfill":
              item = data[0]
              self._fillitem = self._fillpath = None
              if item in self.items:
                  self.screen._delete(item)
                  self.items.remove(item)
          elif action == "pen":
              TPen.pen(self, data[0])
              self.undobuffer.pop()
  
      def undo(self):
          """undo (repeatedly) the last turtle action.
  
          No argument.
  
          undo (repeatedly) the last turtle action.
          Number of available undo actions is determined by the size of
          the undobuffer.
  
          Example (for a Turtle instance named turtle):
          >>> for i in range(4):
          ...     turtle.fd(50); turtle.lt(80)
          ...
          >>> for i in range(8):
          ...     turtle.undo()
          ...
          """
          if self.undobuffer is None:
              return
          item = self.undobuffer.pop()
          action = item[0]
          data = item[1:]
          if action == "seq":
              while data:
                  item = data.pop()
                  self._undo(item[0], item[1:])
          else:
              self._undo(action, data)
  
      turtlesize = shapesize
  
  RawPen = RawTurtle
  
  ###  Screen - Singleton  ########################
  
  def Screen():
      """Return the singleton screen object.
      If none exists at the moment, create a new one and return it,
      else return the existing one."""
      if Turtle._screen is None:
          Turtle._screen = _Screen()
      return Turtle._screen
  
  class _Screen(TurtleScreen):
  
      _root = None
      _canvas = None
      _title = _CFG["title"]
  
      def __init__(self):
          # XXX there is no need for this code to be conditional,
          # as there will be only a single _Screen instance, anyway
          # XXX actually, the turtle demo is injecting root window,
          # so perhaps the conditional creation of a root should be
          # preserved (perhaps by passing it as an optional parameter)
          if _Screen._root is None:
              _Screen._root = self._root = _Root()
              self._root.title(_Screen._title)
              self._root.ondestroy(self._destroy)
          if _Screen._canvas is None:
              width = _CFG["width"]
              height = _CFG["height"]
              canvwidth = _CFG["canvwidth"]
              canvheight = _CFG["canvheight"]
              leftright = _CFG["leftright"]
              topbottom = _CFG["topbottom"]
              self._root.setupcanvas(width, height, canvwidth, canvheight)
              _Screen._canvas = self._root._getcanvas()
              TurtleScreen.__init__(self, _Screen._canvas)
              self.setup(width, height, leftright, topbottom)
  
      def setup(self, width=_CFG["width"], height=_CFG["height"],
                startx=_CFG["leftright"], starty=_CFG["topbottom"]):
          """ Set the size and position of the main window.
  
          Arguments:
          width: as integer a size in pixels, as float a fraction of the screen.
            Default is 50% of screen.
          height: as integer the height in pixels, as float a fraction of the
            screen. Default is 75% of screen.
          startx: if positive, starting position in pixels from the left
            edge of the screen, if negative from the right edge
            Default, startx=None is to center window horizontally.
          starty: if positive, starting position in pixels from the top
            edge of the screen, if negative from the bottom edge
            Default, starty=None is to center window vertically.
  
          Examples (for a Screen instance named screen):
          >>> screen.setup (width=200, height=200, startx=0, starty=0)
  
          sets window to 200x200 pixels, in upper left of screen
  
          >>> screen.setup(width=.75, height=0.5, startx=None, starty=None)
  
          sets window to 75% of screen by 50% of screen and centers
          """
          if not hasattr(self._root, "set_geometry"):
              return
          sw = self._root.win_width()
          sh = self._root.win_height()
          if isinstance(width, float) and 0 <= width <= 1:
              width = sw*width
          if startx is None:
              startx = (sw - width) / 2
          if isinstance(height, float) and 0 <= height <= 1:
              height = sh*height
          if starty is None:
              starty = (sh - height) / 2
          self._root.set_geometry(width, height, startx, starty)
          self.update()
  
      def title(self, titlestring):
          """Set title of turtle-window
  
          Argument:
          titlestring -- a string, to appear in the titlebar of the
                         turtle graphics window.
  
          This is a method of Screen-class. Not available for TurtleScreen-
          objects.
  
          Example (for a Screen instance named screen):
          >>> screen.title("Welcome to the turtle-zoo!")
          """
          if _Screen._root is not None:
              _Screen._root.title(titlestring)
          _Screen._title = titlestring
  
      def _destroy(self):
          root = self._root
          if root is _Screen._root:
              Turtle._pen = None
              Turtle._screen = None
              _Screen._root = None
              _Screen._canvas = None
          TurtleScreen._RUNNING = False
          root.destroy()
  
      def bye(self):
          """Shut the turtlegraphics window.
  
          Example (for a TurtleScreen instance named screen):
          >>> screen.bye()
          """
          self._destroy()
  
      def exitonclick(self):
          """Go into mainloop until the mouse is clicked.
  
          No arguments.
  
          Bind bye() method to mouseclick on TurtleScreen.
          If "using_IDLE" - value in configuration dictionary is False
          (default value), enter mainloop.
          If IDLE with -n switch (no subprocess) is used, this value should be
          set to True in turtle.cfg. In this case IDLE's mainloop
          is active also for the client script.
  
          This is a method of the Screen-class and not available for
          TurtleScreen instances.
  
          Example (for a Screen instance named screen):
          >>> screen.exitonclick()
  
          """
          def exitGracefully(x, y):
              """Screen.bye() with two dummy-parameters"""
              self.bye()
          self.onclick(exitGracefully)
          if _CFG["using_IDLE"]:
              return
          try:
              mainloop()
          except AttributeError:
              exit(0)
  
  class Turtle(RawTurtle):
      """RawTurtle auto-creating (scrolled) canvas.
  
      When a Turtle object is created or a function derived from some
      Turtle method is called a TurtleScreen object is automatically created.
      """
      _pen = None
      _screen = None
  
      def __init__(self,
                   shape=_CFG["shape"],
                   undobuffersize=_CFG["undobuffersize"],
                   visible=_CFG["visible"]):
          if Turtle._screen is None:
              Turtle._screen = Screen()
          RawTurtle.__init__(self, Turtle._screen,
                             shape=shape,
                             undobuffersize=undobuffersize,
                             visible=visible)
  
  Pen = Turtle
  
  def write_docstringdict(filename="turtle_docstringdict"):
      """Create and write docstring-dictionary to file.
  
      Optional argument:
      filename -- a string, used as filename
                  default value is turtle_docstringdict
  
      Has to be called explicitly, (not used by the turtle-graphics classes)
      The docstring dictionary will be written to the Python script <filname>.py
      It is intended to serve as a template for translation of the docstrings
      into different languages.
      """
      docsdict = {}
  
      for methodname in _tg_screen_functions:
          key = "_Screen."+methodname
          docsdict[key] = eval(key).__doc__
      for methodname in _tg_turtle_functions:
          key = "Turtle."+methodname
          docsdict[key] = eval(key).__doc__
  
      with open("%s.py" % filename,"w") as f:
          keys = sorted(x for x in docsdict
                        if x.split('.')[1] not in _alias_list)
          f.write('docsdict = {\n\n')
          for key in keys[:-1]:
              f.write('%s :\n' % repr(key))
              f.write('        """%s\n""",\n\n' % docsdict[key])
          key = keys[-1]
          f.write('%s :\n' % repr(key))
          f.write('        """%s\n"""\n\n' % docsdict[key])
          f.write("}\n")
          f.close()
  
  def read_docstrings(lang):
      """Read in docstrings from lang-specific docstring dictionary.
  
      Transfer docstrings, translated to lang, from a dictionary-file
      to the methods of classes Screen and Turtle and - in revised form -
      to the corresponding functions.
      """
      modname = "turtle_docstringdict_%(language)s" % {'language':lang.lower()}
      module = __import__(modname)
      docsdict = module.docsdict
      for key in docsdict:
          try:
  #            eval(key).im_func.__doc__ = docsdict[key]
              eval(key).__doc__ = docsdict[key]
          except Exception:
              print("Bad docstring-entry: %s" % key)
  
  _LANGUAGE = _CFG["language"]
  
  try:
      if _LANGUAGE != "english":
          read_docstrings(_LANGUAGE)
  except ImportError:
      print("Cannot find docsdict for", _LANGUAGE)
  except Exception:
      print ("Unknown Error when trying to import %s-docstring-dictionary" %
                                                                    _LANGUAGE)
  
  
  def getmethparlist(ob):
      """Get strings describing the arguments for the given object
  
      Returns a pair of strings representing function parameter lists
      including parenthesis.  The first string is suitable for use in
      function definition and the second is suitable for use in function
      call.  The "self" parameter is not included.
      """
      defText = callText = ""
      # bit of a hack for methods - turn it into a function
      # but we drop the "self" param.
      # Try and build one for Python defined functions
      args, varargs, varkw = inspect.getargs(ob.__code__)
      items2 = args[1:]
      realArgs = args[1:]
      defaults = ob.__defaults__ or []
      defaults = ["=%r" % (value,) for value in defaults]
      defaults = [""] * (len(realArgs)-len(defaults)) + defaults
      items1 = [arg + dflt for arg, dflt in zip(realArgs, defaults)]
      if varargs is not None:
          items1.append("*" + varargs)
          items2.append("*" + varargs)
      if varkw is not None:
          items1.append("**" + varkw)
          items2.append("**" + varkw)
      defText = ", ".join(items1)
      defText = "(%s)" % defText
      callText = ", ".join(items2)
      callText = "(%s)" % callText
      return defText, callText
  
  def _turtle_docrevise(docstr):
      """To reduce docstrings from RawTurtle class for functions
      """
      import re
      if docstr is None:
          return None
      turtlename = _CFG["exampleturtle"]
      newdocstr = docstr.replace("%s." % turtlename,"")
      parexp = re.compile(r' \(.+ %s\):' % turtlename)
      newdocstr = parexp.sub(":", newdocstr)
      return newdocstr
  
  def _screen_docrevise(docstr):
      """To reduce docstrings from TurtleScreen class for functions
      """
      import re
      if docstr is None:
          return None
      screenname = _CFG["examplescreen"]
      newdocstr = docstr.replace("%s." % screenname,"")
      parexp = re.compile(r' \(.+ %s\):' % screenname)
      newdocstr = parexp.sub(":", newdocstr)
      return newdocstr
  
  ## The following mechanism makes all methods of RawTurtle and Turtle available
  ## as functions. So we can enhance, change, add, delete methods to these
  ## classes and do not need to change anything here.
  
  __func_body = """\
  def {name}{paramslist}:
      if {obj} is None:
          if not TurtleScreen._RUNNING:
              TurtleScreen._RUNNING = True
              raise Terminator
          {obj} = {init}
      try:
          return {obj}.{name}{argslist}
      except TK.TclError:
          if not TurtleScreen._RUNNING:
              TurtleScreen._RUNNING = True
              raise Terminator
          raise
  """
  
  def _make_global_funcs(functions, cls, obj, init, docrevise):
      for methodname in functions:
          method = getattr(cls, methodname)
          pl1, pl2 = getmethparlist(method)
          if pl1 == "":
              print(">>>>>>", pl1, pl2)
              continue
          defstr = __func_body.format(obj=obj, init=init, name=methodname,
                                      paramslist=pl1, argslist=pl2)
          exec(defstr, globals())
          globals()[methodname].__doc__ = docrevise(method.__doc__)
  
  _make_global_funcs(_tg_screen_functions, _Screen,
                     'Turtle._screen', 'Screen()', _screen_docrevise)
  _make_global_funcs(_tg_turtle_functions, Turtle,
                     'Turtle._pen', 'Turtle()', _turtle_docrevise)
  
  
  done = mainloop
  
  if __name__ == "__main__":
      def switchpen():
          if isdown():
              pu()
          else:
              pd()
  
      def demo1():
          """Demo of old turtle.py - module"""
          reset()
          tracer(True)
          up()
          backward(100)
          down()
          # draw 3 squares; the last filled
          width(3)
          for i in range(3):
              if i == 2:
                  begin_fill()
              for _ in range(4):
                  forward(20)
                  left(90)
              if i == 2:
                  color("maroon")
                  end_fill()
              up()
              forward(30)
              down()
          width(1)
          color("black")
          # move out of the way
          tracer(False)
          up()
          right(90)
          forward(100)
          right(90)
          forward(100)
          right(180)
          down()
          # some text
          write("startstart", 1)
          write("start", 1)
          color("red")
          # staircase
          for i in range(5):
              forward(20)
              left(90)
              forward(20)
              right(90)
          # filled staircase
          tracer(True)
          begin_fill()
          for i in range(5):
              forward(20)
              left(90)
              forward(20)
              right(90)
          end_fill()
          # more text
  
      def demo2():
          """Demo of some new features."""
          speed(1)
          st()
          pensize(3)
          setheading(towards(0, 0))
          radius = distance(0, 0)/2.0
          rt(90)
          for _ in range(18):
              switchpen()
              circle(radius, 10)
          write("wait a moment...")
          while undobufferentries():
              undo()
          reset()
          lt(90)
          colormode(255)
          laenge = 10
          pencolor("green")
          pensize(3)
          lt(180)
          for i in range(-2, 16):
              if i > 0:
                  begin_fill()
                  fillcolor(255-15*i, 0, 15*i)
              for _ in range(3):
                  fd(laenge)
                  lt(120)
              end_fill()
              laenge += 10
              lt(15)
              speed((speed()+1)%12)
          #end_fill()
  
          lt(120)
          pu()
          fd(70)
          rt(30)
          pd()
          color("red","yellow")
          speed(0)
          begin_fill()
          for _ in range(4):
              circle(50, 90)
              rt(90)
              fd(30)
              rt(90)
          end_fill()
          lt(90)
          pu()
          fd(30)
          pd()
          shape("turtle")
  
          tri = getturtle()
          tri.resizemode("auto")
          turtle = Turtle()
          turtle.resizemode("auto")
          turtle.shape("turtle")
          turtle.reset()
          turtle.left(90)
          turtle.speed(0)
          turtle.up()
          turtle.goto(280, 40)
          turtle.lt(30)
          turtle.down()
          turtle.speed(6)
          turtle.color("blue","orange")
          turtle.pensize(2)
          tri.speed(6)
          setheading(towards(turtle))
          count = 1
          while tri.distance(turtle) > 4:
              turtle.fd(3.5)
              turtle.lt(0.6)
              tri.setheading(tri.towards(turtle))
              tri.fd(4)
              if count % 20 == 0:
                  turtle.stamp()
                  tri.stamp()
                  switchpen()
              count += 1
          tri.write("CAUGHT! ", font=("Arial", 16, "bold"), align="right")
          tri.pencolor("black")
          tri.pencolor("red")
  
          def baba(xdummy, ydummy):
              clearscreen()
              bye()
  
          time.sleep(2)
  
          while undobufferentries():
              tri.undo()
              turtle.undo()
          tri.fd(50)
          tri.write("  Click me!", font = ("Courier", 12, "bold") )
          tri.onclick(baba, 1)
  
      demo1()
      demo2()
      exitonclick()
  