text: import math
  
  from browser import console, document
  import _svg
  
  _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,
          "turtle_div_id": "turtle-div",
          "turtle_canvas_id": "turtle-canvas"
         }
  
  def set_defaults(**params):
      _CFG.update(**params)
  
  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     ###
  ##############################################################################
  
  class _Root:
      """Root class for Screen based on Tkinter."""
  
      def setupcanvas(self, width, height, cwidth, cheight):
          self._svg=_svg.svg(Id=_CFG["turtle_canvas_id"], width=cwidth, height=cheight)
          self._canvas=_svg.g(transform="translate(%d,%d)" % (cwidth//2, cheight//2))
          self._svg <= self._canvas
  
      def end(self):
          def set_svg():
              #have to do this to get animate to work...
              document[_CFG['turtle_div_id']].html=document[_CFG['turtle_div_id']].html
          if _CFG["turtle_canvas_id"] not in document:
              document[_CFG["turtle_div_id"]] <= self._svg
              from browser import timer
          #need this for chrome so that first few draw commands are viewed properly.
          timer.set_timeout(set_svg, 1)
  
      def _getcanvas(self):
          return self._canvas
  
      def win_width(self):
          return self._canvas.width
  
      def win_height(self):
          return self._canvas.height
  
  class TurtleScreenBase:
      """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
      #    """
      #    pass
  
      #@staticmethod
      #def _image(filename):
      #    """return an image object containing the
      #    imagedata from a gif-file named filename.
      #    """
      #    pass
  
      def __init__(self, cv):
          self.cv = cv
  
          self._previous_turtle_attributes={}
          self._draw_pos=0
  
          self.canvwidth = cv.parentElement.width
          self.canvheight = cv.parentElement.height
          self.xscale = self.yscale = 1.0
  
      def _createpoly(self):
          """Create an invisible polygon item on canvas self.cv)
          """
          #console.log("_createpoly")
          pass
  
      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.
          """
          #console.log("_drawpoly")
          pass
  
      def _drawline(self, lineitem, coordlist=None,
                    fill=None, width=None, top=False,
                    speed=None):
          """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.
          """
  
          #console.log("_drawline")
          #if not isinstance(lineitem, Turtle):
          #   return
  
          if coordlist is not None:
             _x0, _y0=coordlist[0]
             _x1, _y1=coordlist[1]
  
             _dist=math.sqrt( (_x0-_x1)*(_x0-_x1) + (_y0-_y1)*(_y0-_y1) )
  
             if speed is not None:
                 if speed == 0:
                     speed = 10
                 _dist /= (speed/2)
  
             _dur="%4.2fs" % (0.01*_dist)
             if _dur == '0.00s':
                _dur='0.1s'
  
  
  
             #_dur="%ss" % 1
             self._draw_pos+=1
  
             _shape=["%s,%s" % (_x, _y) for _x,_y in lineitem.get_shapepoly()]
  
             if 0:
                #if lineitem.isvisible():
                if lineitem in self._previous_turtle_attributes:
                   _previous=self._previous_turtle_attributes[lineitem]
                   if _previous.heading() != lineitem.heading():
                   #if self._turtle_heading[lineitem] != lineitem.heading():
  
                      _rotate=_previous.heading()
                      _turtle=_svg.polygon(points=" ".join(_shape),
                                     transform="rotate(%s)" % (_rotate-90),
                                     style={'stroke': fill, 'fill': fill,
                                            'stroke-width': width, 'display': 'none'})
  
                      # we need to rotate our turtle..
                      _turtle <= _svg.animateTransform(
                                                       Id="animateLine%s" % self._draw_pos,
                                                       attributeName="transform",
                                                       type="rotate",
                                                       attributeType="XML",
                                                       From=_rotate - 90,
                                                       to=lineitem.heading() -90,
                                                       dur=_dur,
                                                       begin="animateLine%s.end" % (self._draw_pos-1))
  
                      _turtle <= _svg.set(attributeName="display",
                                          attributeType="CSS", to="block",
                                          begin="animateLine%s.begin" % self._draw_pos,
                                          end="animateLine%s.end" % self._draw_pos)
  
                      #_turtle <= _svg.animateMotion(From="%s,%s" % (_x0*self.xscale, _y0*self.yscale),
                      #                    to="%s,%s" % (_x0*self.xscale, _y0*self.yscale),
                      #                    begin="animateLine%s.begin" % self._draw_pos,
                      #                    end="animateLine%s.end" % self._draw_pos)
  
                      #_turtle <= _svg.animate(attributeName="fill",
                      #                        From=_previous.fill, to=fill, dur=_dur,
                      #                        begin="animateLine%s.begin" % self._draw_pos)
  
                      self._draw_pos+=1
                      self._canvas <= _turtle
  
  
             _line= _svg.line(x1=_x0*self.xscale, y1=_y0*self.yscale,
                              x2=_x0*self.xscale, y2=_y0*self.yscale,
                              style={'stroke': fill, 'stroke-width': width})
  
             _an1=_svg.animate(Id="animateLine%s" % self._draw_pos,
                               attributeName="x2", attributeType="XML",
                               From=_x0*self.xscale, to=_x1*self.xscale,
                               dur=_dur, fill='freeze')
  
             _an2=_svg.animate(attributeName="y2", attributeType="XML",
                               begin="animateLine%s.begin" % self._draw_pos,
                               From=_y0*self.xscale, to=_y1*self.xscale,
                               dur=_dur, fill='freeze')
  
             # draw turtle
             if lineitem.isvisible():
                _turtle=_svg.polygon(points=" ".join(_shape),
                                     transform="rotate(%s)" % (lineitem.heading() - 90),
                                     style={'stroke': fill, 'fill': fill,
                                            'stroke-width': width, 'display': 'none'})
  
                _turtle <= _svg.animateMotion(From="%s,%s" % (_x0*self.xscale, _y0*self.yscale),
                                          to="%s,%s" % (_x1*self.xscale, _y1*self.yscale),
                                          dur=_dur, begin="animateLine%s.begin" % self._draw_pos)
  
                _turtle <= _svg.set(attributeName="display", attributeType="CSS",
                                  to="block",
                                  begin="animateLine%s.begin" % self._draw_pos,
                                  end="animateLine%s.end" % self._draw_pos)
  
                self._canvas <= _turtle
  
             self._previous_turtle_attributes[lineitem]=lineitem
  
             if self._draw_pos == 1:
                _an1.setAttribute('begin', "0s")
             else:
                _an1.setAttribute('begin', "animateLine%s.end" % (self._draw_pos-1))
  
             _line <= _an1
             _line <= _an2
  
             self._canvas <= _line
  
      def _delete(self, item):
          """Delete graphics item from canvas.
          If item is"all" delete all graphics items.
          """
          pass
  
      def _update(self):
          """Redraw graphics items on canvas
          """
          pass
  
      def _delay(self, delay):
          """Delay subsequent canvas actions for delay ms."""
          pass
  
      def _iscolorstring(self, color):
          """Check if the string color is a legal Tkinter color string.
          """
          return True   #fix me
  
          #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.style.backgroundColor=color
          else:
              return self.cv.style.backgroundColor
  
      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."""
  
          self._draw_pos+=1
          _text= _svg.text(txt, x=pos[0], y=pos[1], fill=pencolor,
                           style={'display': 'none'})
          _text <= _svg.animate(Id="animateLine%s" % self._draw_pos,
                                attributeName="display", attributeType="CSS",
                                From="block", to="block", dur="1s", fill='freeze',
                                begin="animateLine%s.end" % (self._draw_pos-1))
  
          self._canvas <= _text
          return Vec2D(pos[0]+50, pos[1]+50)  #fix me
  
  ##    def _dot(self, pos, size, color):
  ##        """may be implemented for some other graphics toolkit"""
  
      def _createimage(self, image):
          """Create and return image item on canvas.
          """
          pass
  
      def _drawimage(self, item, pos, image):
          """Configure image item as to draw image object
          at position (x,y) on canvas)
          """
          pass
  
      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 ."""
          pass
  
      def _type(self, item):
          """Return 'line' or 'polygon' or 'image' depending on
          type of item.
          """
          pass
  
  
      def _resize(self, canvwidth=None, canvheight=None, bg=None):
          """Resize the canvas the turtles are drawing on. Does
          not alter the drawing window.
          """
          self.cv.style.width=canvwidth
          self.cv.style.height=canvheight
          if bg is not None:
             self.cv.style.backgroundColor=bg
  
      def _window_size(self):
          """ Return the width and height of the turtle window.
          """
          #for now just return canvas width/height
          return self.cv.width, self.cv.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()
  
          """
          pass
  
      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:")
  
          """
          pass
  
      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 imput
          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)
  
          """
          pass
  
  
  ##############################################################################
  ###                  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
      """
      pass
  
  class Shape:
      """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 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", None) #self._blankimage())
                    }
  
          self._bgpics = {"nopic" : ""}
          TurtleScreenBase.__init__(self, cv)
          self._mode = mode
          self._delayvalue = delay
          self._colormode = _CFG["colormode"]
          self._keys = []
          self.clear()
  
      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 -- on 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:
              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._RUNNNING = True
              raise Terminator
          if self._tracing > 0:
              self._updatecounter += 1
              self._updatecounter %= self._tracing
  
      def update(self):
          """Perform a TurtleScreen update.
          """
          return
          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.
          num -- 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:
      """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. Dafault 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"""
          #console.log('_go')
          ende = self._position + self._orient * distance
          self._goto(ende)
  
      def _rotate(self, angle):
          """Turn turtle counterclockwise by specified angle if angle > 0."""
          #console.log('_rotate')
          angle *= self._degreesPerAU
          self._orient = self._orient.rotate(angle)
  
      def _goto(self, end):
          """move turtle to position end."""
          #console.log('_goto')
          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:
      """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 mor 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
                 }
  
          #console.log('pen')
          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:
      """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):
          #console.log("_setshape", self._type)
          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
          return
          #console.log(self._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]
          #console.log(self._item)
  
  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 = None #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:
              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.
          """
          return
          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:
              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 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)
          """
          #console.log("shapetransform")
          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._update()
  
  
      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."""
          return
  
  ##############################  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.
          """
  
          if self._speed and self.screen._tracing == 1:
              if self._drawing:
                 #console.log('%s:%s:%s:%s:%s' % (self, start, end, self._pencolor,
                 #                                self._pensize))
                 self.screen._drawline(self,     #please remove me eventually
                                  (self._position, end),
                                  self._pencolor, self._pensize,
                                  False,
                                  self._speed)
  
          if isinstance(self._fillpath, list):
              self._fillpath.append(end)
          ######    vererbung!!!!!!!!!!!!!!!!!!!!!!
          self._position = end
  
      def _rotate(self, angle):
          """Turns pen clockwise by angle.
          """
          #console.log('_rotate')
          if self.undobuffer:
              self.undobuffer.push(("rot", angle, self._degreesPerAU))
          angle *= self._degreesPerAU
          neworient = self._orient.rotate(angle)
          tracing = self.screen._tracing
  
          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.
          """
          #console.log('_newLine')
          return
  
      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)
  
      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 end(self):
          self._root.end()
  
      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()
  
  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 _getpen():
      """Create the 'anonymous' turtle if not already present."""
      if Turtle._pen is None:
          Turtle._pen = Turtle()
      return Turtle._pen
  
  def _getscreen():
      """Create a TurtleScreen if not already present."""
      if Turtle._screen is None:
          Turtle._screen = Screen()
      return Turtle._screen
  
  def restart():
      _Screen._root = None
      _Screen._canvas = None
      Turtle._screen = None
  