text: """An abstract base class for console-type widgets."""
  
  # Copyright (c) Jupyter Development Team.
  # Distributed under the terms of the Modified BSD License.
  
  import os.path
  import re
  import sys
  from textwrap import dedent
  import time
  from unicodedata import category
  import webbrowser
  
  from qtconsole.qt import QtCore, QtGui
  
  from traitlets.config.configurable import LoggingConfigurable
  from qtconsole.rich_text import HtmlExporter
  from qtconsole.util import MetaQObjectHasTraits, get_font
  from ipython_genutils.text import columnize
  from traitlets import Bool, Enum, Integer, Unicode
  from .ansi_code_processor import QtAnsiCodeProcessor
  from .completion_widget import CompletionWidget
  from .completion_html import CompletionHtml
  from .completion_plain import CompletionPlain
  from .kill_ring import QtKillRing
  
  
  def is_letter_or_number(char):
      """ Returns whether the specified unicode character is a letter or a number.
      """
      cat = category(char)
      return cat.startswith('L') or cat.startswith('N')
  
  #-----------------------------------------------------------------------------
  # Classes
  #-----------------------------------------------------------------------------
  
  class ConsoleWidget(MetaQObjectHasTraits('NewBase', (LoggingConfigurable, QtGui.QWidget), {})):
      """ An abstract base class for console-type widgets. This class has
          functionality for:
  
              * Maintaining a prompt and editing region
              * Providing the traditional Unix-style console keyboard shortcuts
              * Performing tab completion
              * Paging text
              * Handling ANSI escape codes
  
          ConsoleWidget also provides a number of utility methods that will be
          convenient to implementors of a console-style widget.
      """
  
      #------ Configuration ------------------------------------------------------
  
      ansi_codes = Bool(True, config=True,
          help="Whether to process ANSI escape codes."
      )
      buffer_size = Integer(500, config=True,
          help="""
          The maximum number of lines of text before truncation. Specifying a
          non-positive number disables text truncation (not recommended).
          """
      )
      execute_on_complete_input = Bool(True, config=True,
          help="""Whether to automatically execute on syntactically complete input.
          
          If False, Shift-Enter is required to submit each execution.
          Disabling this is mainly useful for non-Python kernels,
          where the completion check would be wrong.
          """
      )
      gui_completion = Enum(['plain', 'droplist', 'ncurses'], config=True,
                      default_value = 'ncurses',
                      help="""
                      The type of completer to use. Valid values are:
  
                      'plain'   : Show the available completion as a text list
                                  Below the editing area.
                      'droplist': Show the completion in a drop down list navigable
                                  by the arrow keys, and from which you can select
                                  completion by pressing Return.
                      'ncurses' : Show the completion as a text list which is navigable by
                                  `tab` and arrow keys.
                      """
      )
      # NOTE: this value can only be specified during initialization.
      kind = Enum(['plain', 'rich'], default_value='plain', config=True,
          help="""
          The type of underlying text widget to use. Valid values are 'plain',
          which specifies a QPlainTextEdit, and 'rich', which specifies a
          QTextEdit.
          """
      )
      # NOTE: this value can only be specified during initialization.
      paging = Enum(['inside', 'hsplit', 'vsplit', 'custom', 'none'],
                    default_value='inside', config=True,
          help="""
          The type of paging to use. Valid values are:
  
          'inside'
             The widget pages like a traditional terminal.
          'hsplit'
             When paging is requested, the widget is split horizontally. The top
             pane contains the console, and the bottom pane contains the paged text.
          'vsplit'
             Similar to 'hsplit', except that a vertical splitter is used.
          'custom'
             No action is taken by the widget beyond emitting a
             'custom_page_requested(str)' signal.
          'none'
             The text is written directly to the console.
          """)
  
      font_family = Unicode(config=True,
          help="""The font family to use for the console.
          On OSX this defaults to Monaco, on Windows the default is
          Consolas with fallback of Courier, and on other platforms
          the default is Monospace.
          """)
      def _font_family_default(self):
          if sys.platform == 'win32':
              # Consolas ships with Vista/Win7, fallback to Courier if needed
              return 'Consolas'
          elif sys.platform == 'darwin':
              # OSX always has Monaco, no need for a fallback
              return 'Monaco'
          else:
              # Monospace should always exist, no need for a fallback
              return 'Monospace'
  
      font_size = Integer(config=True,
          help="""The font size. If unconfigured, Qt will be entrusted
          with the size of the font.
          """)
  
      width = Integer(81, config=True,
          help="""The width of the console at start time in number
          of characters (will double with `hsplit` paging)
          """)
  
      height = Integer(25, config=True,
          help="""The height of the console at start time in number
          of characters (will double with `vsplit` paging)
          """)
  
      # Whether to override ShortcutEvents for the keybindings defined by this
      # widget (Ctrl+n, Ctrl+a, etc). Enable this if you want this widget to take
      # priority (when it has focus) over, e.g., window-level menu shortcuts.
      override_shortcuts = Bool(False)
      
      # ------ Custom Qt Widgets -------------------------------------------------
      
      # For other projects to easily override the Qt widgets used by the console
      # (e.g. Spyder)
      custom_control = None
      custom_page_control = None
  
      #------ Signals ------------------------------------------------------------
  
      # Signals that indicate ConsoleWidget state.
      copy_available = QtCore.Signal(bool)
      redo_available = QtCore.Signal(bool)
      undo_available = QtCore.Signal(bool)
  
      # Signal emitted when paging is needed and the paging style has been
      # specified as 'custom'.
      custom_page_requested = QtCore.Signal(object)
  
      # Signal emitted when the font is changed.
      font_changed = QtCore.Signal(QtGui.QFont)
  
      #------ Protected class variables ------------------------------------------
  
      # control handles
      _control = None
      _page_control = None
      _splitter = None
  
      # When the control key is down, these keys are mapped.
      _ctrl_down_remap = { QtCore.Qt.Key_B : QtCore.Qt.Key_Left,
                           QtCore.Qt.Key_F : QtCore.Qt.Key_Right,
                           QtCore.Qt.Key_A : QtCore.Qt.Key_Home,
                           QtCore.Qt.Key_P : QtCore.Qt.Key_Up,
                           QtCore.Qt.Key_N : QtCore.Qt.Key_Down,
                           QtCore.Qt.Key_H : QtCore.Qt.Key_Backspace, }
      if not sys.platform == 'darwin':
          # On OS X, Ctrl-E already does the right thing, whereas End moves the
          # cursor to the bottom of the buffer.
          _ctrl_down_remap[QtCore.Qt.Key_E] = QtCore.Qt.Key_End
  
      # The shortcuts defined by this widget. We need to keep track of these to
      # support 'override_shortcuts' above.
      _shortcuts = set(_ctrl_down_remap.keys()) | \
                       { QtCore.Qt.Key_C, QtCore.Qt.Key_G, QtCore.Qt.Key_O,
                         QtCore.Qt.Key_V }
  
      _temp_buffer_filled = False
  
      #---------------------------------------------------------------------------
      # 'QObject' interface
      #---------------------------------------------------------------------------
  
      def __init__(self, parent=None, **kw):
          """ Create a ConsoleWidget.
  
          Parameters
          ----------
          parent : QWidget, optional [default None]
              The parent for this widget.
          """
          QtGui.QWidget.__init__(self, parent)
          LoggingConfigurable.__init__(self, **kw)
  
          # While scrolling the pager on Mac OS X, it tears badly.  The
          # NativeGesture is platform and perhaps build-specific hence
          # we take adequate precautions here.
          self._pager_scroll_events = [QtCore.QEvent.Wheel]
          if hasattr(QtCore.QEvent, 'NativeGesture'):
              self._pager_scroll_events.append(QtCore.QEvent.NativeGesture)
  
          # Create the layout and underlying text widget.
          layout = QtGui.QStackedLayout(self)
          layout.setContentsMargins(0, 0, 0, 0)
          self._control = self._create_control()
          if self.paging in ('hsplit', 'vsplit'):
              self._splitter = QtGui.QSplitter()
              if self.paging == 'hsplit':
                  self._splitter.setOrientation(QtCore.Qt.Horizontal)
              else:
                  self._splitter.setOrientation(QtCore.Qt.Vertical)
              self._splitter.addWidget(self._control)
              layout.addWidget(self._splitter)
          else:
              layout.addWidget(self._control)
  
          # Create the paging widget, if necessary.
          if self.paging in ('inside', 'hsplit', 'vsplit'):
              self._page_control = self._create_page_control()
              if self._splitter:
                  self._page_control.hide()
                  self._splitter.addWidget(self._page_control)
              else:
                  layout.addWidget(self._page_control)
  
          # Initialize protected variables. Some variables contain useful state
          # information for subclasses; they should be considered read-only.
          self._append_before_prompt_pos = 0
          self._ansi_processor = QtAnsiCodeProcessor()
          if self.gui_completion == 'ncurses':
              self._completion_widget = CompletionHtml(self)
          elif self.gui_completion == 'droplist':
              self._completion_widget = CompletionWidget(self)
          elif self.gui_completion == 'plain':
              self._completion_widget = CompletionPlain(self)
  
          self._continuation_prompt = '> '
          self._continuation_prompt_html = None
          self._executing = False
          self._filter_resize = False
          self._html_exporter = HtmlExporter(self._control)
          self._input_buffer_executing = ''
          self._input_buffer_pending = ''
          self._kill_ring = QtKillRing(self._control)
          self._prompt = ''
          self._prompt_html = None
          self._prompt_pos = 0
          self._prompt_sep = ''
          self._reading = False
          self._reading_callback = None
          self._tab_width = 8
  
          # List of strings pending to be appended as plain text in the widget.
          # The text is not immediately inserted when available to not
          # choke the Qt event loop with paint events for the widget in
          # case of lots of output from kernel.
          self._pending_insert_text = []
  
          # Timer to flush the pending stream messages. The interval is adjusted
          # later based on actual time taken for flushing a screen (buffer_size)
          # of output text.
          self._pending_text_flush_interval = QtCore.QTimer(self._control)
          self._pending_text_flush_interval.setInterval(100)
          self._pending_text_flush_interval.setSingleShot(True)
          self._pending_text_flush_interval.timeout.connect(
                                              self._on_flush_pending_stream_timer)
  
          # Set a monospaced font.
          self.reset_font()
  
          # Configure actions.
          action = QtGui.QAction('Print', None)
          action.setEnabled(True)
          printkey = QtGui.QKeySequence(QtGui.QKeySequence.Print)
          if printkey.matches("Ctrl+P") and sys.platform != 'darwin':
              # Only override the default if there is a collision.
              # Qt ctrl = cmd on OSX, so the match gets a false positive on OSX.
              printkey = "Ctrl+Shift+P"
          action.setShortcut(printkey)
          action.setShortcutContext(QtCore.Qt.WidgetWithChildrenShortcut)
          action.triggered.connect(self.print_)
          self.addAction(action)
          self.print_action = action
  
          action = QtGui.QAction('Save as HTML/XML', None)
          action.setShortcut(QtGui.QKeySequence.Save)
          action.setShortcutContext(QtCore.Qt.WidgetWithChildrenShortcut)
          action.triggered.connect(self.export_html)
          self.addAction(action)
          self.export_action = action
  
          action = QtGui.QAction('Select All', None)
          action.setEnabled(True)
          selectall = QtGui.QKeySequence(QtGui.QKeySequence.SelectAll)
          if selectall.matches("Ctrl+A") and sys.platform != 'darwin':
              # Only override the default if there is a collision.
              # Qt ctrl = cmd on OSX, so the match gets a false positive on OSX.
              selectall = "Ctrl+Shift+A"
          action.setShortcut(selectall)
          action.setShortcutContext(QtCore.Qt.WidgetWithChildrenShortcut)
          action.triggered.connect(self.select_all)
          self.addAction(action)
          self.select_all_action = action
  
          self.increase_font_size = QtGui.QAction("Bigger Font",
                  self,
                  shortcut=QtGui.QKeySequence.ZoomIn,
                  shortcutContext=QtCore.Qt.WidgetWithChildrenShortcut,
                  statusTip="Increase the font size by one point",
                  triggered=self._increase_font_size)
          self.addAction(self.increase_font_size)
  
          self.decrease_font_size = QtGui.QAction("Smaller Font",
                  self,
                  shortcut=QtGui.QKeySequence.ZoomOut,
                  shortcutContext=QtCore.Qt.WidgetWithChildrenShortcut,
                  statusTip="Decrease the font size by one point",
                  triggered=self._decrease_font_size)
          self.addAction(self.decrease_font_size)
  
          self.reset_font_size = QtGui.QAction("Normal Font",
                  self,
                  shortcut="Ctrl+0",
                  shortcutContext=QtCore.Qt.WidgetWithChildrenShortcut,
                  statusTip="Restore the Normal font size",
                  triggered=self.reset_font)
          self.addAction(self.reset_font_size)
  
          # Accept drag and drop events here. Drops were already turned off
          # in self._control when that widget was created.
          self.setAcceptDrops(True)
  
      #---------------------------------------------------------------------------
      # Drag and drop support
      #---------------------------------------------------------------------------
  
      def dragEnterEvent(self, e):
          if e.mimeData().hasUrls():
              # The link action should indicate to that the drop will insert
              # the file anme.
              e.setDropAction(QtCore.Qt.LinkAction)
              e.accept()
          elif e.mimeData().hasText():
              # By changing the action to copy we don't need to worry about
              # the user accidentally moving text around in the widget.
              e.setDropAction(QtCore.Qt.CopyAction)
              e.accept()
  
      def dragMoveEvent(self, e):
          if e.mimeData().hasUrls():
              pass
          elif e.mimeData().hasText():
              cursor = self._control.cursorForPosition(e.pos())
              if self._in_buffer(cursor.position()):
                  e.setDropAction(QtCore.Qt.CopyAction)
                  self._control.setTextCursor(cursor)
              else:
                  e.setDropAction(QtCore.Qt.IgnoreAction)
              e.accept()
  
      def dropEvent(self, e):
          if e.mimeData().hasUrls():
              self._keep_cursor_in_buffer()
              cursor = self._control.textCursor()
              filenames = [url.toLocalFile() for url in e.mimeData().urls()]
              text = ', '.join("'" + f.replace("'", "'\"'\"'") + "'"
                               for f in filenames)
              self._insert_plain_text_into_buffer(cursor, text)
          elif e.mimeData().hasText():
              cursor = self._control.cursorForPosition(e.pos())
              if self._in_buffer(cursor.position()):
                  text = e.mimeData().text()
                  self._insert_plain_text_into_buffer(cursor, text)
  
      def eventFilter(self, obj, event):
          """ Reimplemented to ensure a console-like behavior in the underlying
              text widgets.
          """
          etype = event.type()
          if etype == QtCore.QEvent.KeyPress:
  
              # Re-map keys for all filtered widgets.
              key = event.key()
              if self._control_key_down(event.modifiers()) and \
                      key in self._ctrl_down_remap:
                  new_event = QtGui.QKeyEvent(QtCore.QEvent.KeyPress,
                                              self._ctrl_down_remap[key],
                                              QtCore.Qt.NoModifier)
                  QtGui.qApp.sendEvent(obj, new_event)
                  return True
  
              elif obj == self._control:
                  return self._event_filter_console_keypress(event)
  
              elif obj == self._page_control:
                  return self._event_filter_page_keypress(event)
  
          # Make middle-click paste safe.
          elif etype == QtCore.QEvent.MouseButtonRelease and \
                  event.button() == QtCore.Qt.MidButton and \
                  obj == self._control.viewport():
              cursor = self._control.cursorForPosition(event.pos())
              self._control.setTextCursor(cursor)
              self.paste(QtGui.QClipboard.Selection)
              return True
  
          # Manually adjust the scrollbars *after* a resize event is dispatched.
          elif etype == QtCore.QEvent.Resize and not self._filter_resize:
              self._filter_resize = True
              QtGui.qApp.sendEvent(obj, event)
              self._adjust_scrollbars()
              self._filter_resize = False
              return True
  
          # Override shortcuts for all filtered widgets.
          elif etype == QtCore.QEvent.ShortcutOverride and \
                  self.override_shortcuts and \
                  self._control_key_down(event.modifiers()) and \
                  event.key() in self._shortcuts:
              event.accept()
  
          # Handle scrolling of the vsplit pager. This hack attempts to solve
          # problems with tearing of the help text inside the pager window.  This
          # happens only on Mac OS X with both PySide and PyQt. This fix isn't
          # perfect but makes the pager more usable.
          elif etype in self._pager_scroll_events and \
                  obj == self._page_control:
              self._page_control.repaint()
              return True
  
          elif etype == QtCore.QEvent.MouseMove:
              anchor = self._control.anchorAt(event.pos())
              QtGui.QToolTip.showText(event.globalPos(), anchor)
  
          return super(ConsoleWidget, self).eventFilter(obj, event)
  
      #---------------------------------------------------------------------------
      # 'QWidget' interface
      #---------------------------------------------------------------------------
  
      def sizeHint(self):
          """ Reimplemented to suggest a size that is 80 characters wide and
              25 lines high.
          """
          font_metrics = QtGui.QFontMetrics(self.font)
          margin = (self._control.frameWidth() +
                    self._control.document().documentMargin()) * 2
          style = self.style()
          splitwidth = style.pixelMetric(QtGui.QStyle.PM_SplitterWidth)
  
          # Note 1: Despite my best efforts to take the various margins into
          # account, the width is still coming out a bit too small, so we include
          # a fudge factor of one character here.
          # Note 2: QFontMetrics.maxWidth is not used here or anywhere else due
          # to a Qt bug on certain Mac OS systems where it returns 0.
          width = font_metrics.width(' ') * self.width + margin
          width += style.pixelMetric(QtGui.QStyle.PM_ScrollBarExtent)
          if self.paging == 'hsplit':
              width = width * 2 + splitwidth
  
          height = font_metrics.height() * self.height + margin
          if self.paging == 'vsplit':
              height = height * 2 + splitwidth
  
          return QtCore.QSize(width, height)
  
      #---------------------------------------------------------------------------
      # 'ConsoleWidget' public interface
      #---------------------------------------------------------------------------
      
      include_other_output = Bool(False, config=True,
          help="""Whether to include output from clients
          other than this one sharing the same kernel.
          
          Outputs are not displayed until enter is pressed.
          """
      )
      
      def can_copy(self):
          """ Returns whether text can be copied to the clipboard.
          """
          return self._control.textCursor().hasSelection()
  
      def can_cut(self):
          """ Returns whether text can be cut to the clipboard.
          """
          cursor = self._control.textCursor()
          return (cursor.hasSelection() and
                  self._in_buffer(cursor.anchor()) and
                  self._in_buffer(cursor.position()))
  
      def can_paste(self):
          """ Returns whether text can be pasted from the clipboard.
          """
          if self._control.textInteractionFlags() & QtCore.Qt.TextEditable:
              return bool(QtGui.QApplication.clipboard().text())
          return False
  
      def clear(self, keep_input=True):
          """ Clear the console.
  
          Parameters
          ----------
          keep_input : bool, optional (default True)
              If set, restores the old input buffer if a new prompt is written.
          """
          if self._executing:
              self._control.clear()
          else:
              if keep_input:
                  input_buffer = self.input_buffer
              self._control.clear()
              self._show_prompt()
              if keep_input:
                  self.input_buffer = input_buffer
  
      def copy(self):
          """ Copy the currently selected text to the clipboard.
          """
          self.layout().currentWidget().copy()
  
      def copy_anchor(self, anchor):
          """ Copy anchor text to the clipboard
          """
          QtGui.QApplication.clipboard().setText(anchor)
  
      def cut(self):
          """ Copy the currently selected text to the clipboard and delete it
              if it's inside the input buffer.
          """
          self.copy()
          if self.can_cut():
              self._control.textCursor().removeSelectedText()
  
      def execute(self, source=None, hidden=False, interactive=False):
          """ Executes source or the input buffer, possibly prompting for more
          input.
  
          Parameters
          ----------
          source : str, optional
  
              The source to execute. If not specified, the input buffer will be
              used. If specified and 'hidden' is False, the input buffer will be
              replaced with the source before execution.
  
          hidden : bool, optional (default False)
  
              If set, no output will be shown and the prompt will not be modified.
              In other words, it will be completely invisible to the user that
              an execution has occurred.
  
          interactive : bool, optional (default False)
  
              Whether the console is to treat the source as having been manually
              entered by the user. The effect of this parameter depends on the
              subclass implementation.
  
          Raises
          ------
          RuntimeError
              If incomplete input is given and 'hidden' is True. In this case,
              it is not possible to prompt for more input.
  
          Returns
          -------
          A boolean indicating whether the source was executed.
          """
          # WARNING: The order in which things happen here is very particular, in
          # large part because our syntax highlighting is fragile. If you change
          # something, test carefully!
  
          # Decide what to execute.
          if source is None:
              source = self.input_buffer
              if not hidden:
                  # A newline is appended later, but it should be considered part
                  # of the input buffer.
                  source += '\n'
          elif not hidden:
              self.input_buffer = source
  
          # Execute the source or show a continuation prompt if it is incomplete.
          if interactive and self.execute_on_complete_input:
              complete, indent = self._is_complete(source, interactive)
          else:
              complete = True
              indent = ''
          if hidden:
              if complete or not self.execute_on_complete_input:
                  self._execute(source, hidden)
              else:
                  error = 'Incomplete noninteractive input: "%s"'
                  raise RuntimeError(error % source)
          else:
              if complete:
                  self._append_plain_text('\n')
                  self._input_buffer_executing = self.input_buffer
                  self._executing = True
                  self._prompt_finished()
  
                  # The maximum block count is only in effect during execution.
                  # This ensures that _prompt_pos does not become invalid due to
                  # text truncation.
                  self._control.document().setMaximumBlockCount(self.buffer_size)
  
                  # Setting a positive maximum block count will automatically
                  # disable the undo/redo history, but just to be safe:
                  self._control.setUndoRedoEnabled(False)
  
                  # Perform actual execution.
                  self._execute(source, hidden)
  
              else:
                  # Do this inside an edit block so continuation prompts are
                  # removed seamlessly via undo/redo.
                  cursor = self._get_end_cursor()
                  cursor.beginEditBlock()
                  cursor.insertText('\n')
                  self._insert_continuation_prompt(cursor, indent)
                  cursor.endEditBlock()
  
                  # Do not do this inside the edit block. It works as expected
                  # when using a QPlainTextEdit control, but does not have an
                  # effect when using a QTextEdit. I believe this is a Qt bug.
                  self._control.moveCursor(QtGui.QTextCursor.End)
  
          return complete
  
      def export_html(self):
          """ Shows a dialog to export HTML/XML in various formats.
          """
          self._html_exporter.export()
  
      def _get_input_buffer(self, force=False):
          """ The text that the user has entered entered at the current prompt.
  
          If the console is currently executing, the text that is executing will
          always be returned.
          """
          # If we're executing, the input buffer may not even exist anymore due to
          # the limit imposed by 'buffer_size'. Therefore, we store it.
          if self._executing and not force:
              return self._input_buffer_executing
  
          cursor = self._get_end_cursor()
          cursor.setPosition(self._prompt_pos, QtGui.QTextCursor.KeepAnchor)
          input_buffer = cursor.selection().toPlainText()
  
          # Strip out continuation prompts.
          return input_buffer.replace('\n' + self._continuation_prompt, '\n')
  
      def _set_input_buffer(self, string):
          """ Sets the text in the input buffer.
  
          If the console is currently executing, this call has no *immediate*
          effect. When the execution is finished, the input buffer will be updated
          appropriately.
          """
          # If we're executing, store the text for later.
          if self._executing:
              self._input_buffer_pending = string
              return
  
          # Remove old text.
          cursor = self._get_end_cursor()
          cursor.beginEditBlock()
          cursor.setPosition(self._prompt_pos, QtGui.QTextCursor.KeepAnchor)
          cursor.removeSelectedText()
  
          # Insert new text with continuation prompts.
          self._insert_plain_text_into_buffer(self._get_prompt_cursor(), string)
          cursor.endEditBlock()
          self._control.moveCursor(QtGui.QTextCursor.End)
  
      input_buffer = property(_get_input_buffer, _set_input_buffer)
  
      def _get_font(self):
          """ The base font being used by the ConsoleWidget.
          """
          return self._control.document().defaultFont()
  
      def _set_font(self, font):
          """ Sets the base font for the ConsoleWidget to the specified QFont.
          """
          font_metrics = QtGui.QFontMetrics(font)
          self._control.setTabStopWidth(self.tab_width * font_metrics.width(' '))
  
          self._completion_widget.setFont(font)
          self._control.document().setDefaultFont(font)
          if self._page_control:
              self._page_control.document().setDefaultFont(font)
  
          self.font_changed.emit(font)
  
      font = property(_get_font, _set_font)
  
      def open_anchor(self, anchor):
          """ Open selected anchor in the default webbrowser
          """
          webbrowser.open( anchor )
  
      def paste(self, mode=QtGui.QClipboard.Clipboard):
          """ Paste the contents of the clipboard into the input region.
  
          Parameters
          ----------
          mode : QClipboard::Mode, optional [default QClipboard::Clipboard]
  
              Controls which part of the system clipboard is used. This can be
              used to access the selection clipboard in X11 and the Find buffer
              in Mac OS. By default, the regular clipboard is used.
          """
          if self._control.textInteractionFlags() & QtCore.Qt.TextEditable:
              # Make sure the paste is safe.
              self._keep_cursor_in_buffer()
              cursor = self._control.textCursor()
  
              # Remove any trailing newline, which confuses the GUI and forces the
              # user to backspace.
              text = QtGui.QApplication.clipboard().text(mode).rstrip()
              self._insert_plain_text_into_buffer(cursor, dedent(text))
  
      def print_(self, printer = None):
          """ Print the contents of the ConsoleWidget to the specified QPrinter.
          """
          if (not printer):
              printer = QtGui.QPrinter()
              if(QtGui.QPrintDialog(printer).exec_() != QtGui.QDialog.Accepted):
                  return
          self._control.print_(printer)
  
      def prompt_to_top(self):
          """ Moves the prompt to the top of the viewport.
          """
          if not self._executing:
              prompt_cursor = self._get_prompt_cursor()
              if self._get_cursor().blockNumber() < prompt_cursor.blockNumber():
                  self._set_cursor(prompt_cursor)
              self._set_top_cursor(prompt_cursor)
  
      def redo(self):
          """ Redo the last operation. If there is no operation to redo, nothing
              happens.
          """
          self._control.redo()
  
      def reset_font(self):
          """ Sets the font to the default fixed-width font for this platform.
          """
          if sys.platform == 'win32':
              # Consolas ships with Vista/Win7, fallback to Courier if needed
              fallback = 'Courier'
          elif sys.platform == 'darwin':
              # OSX always has Monaco
              fallback = 'Monaco'
          else:
              # Monospace should always exist
              fallback = 'Monospace'
          font = get_font(self.font_family, fallback)
          if self.font_size:
              font.setPointSize(self.font_size)
          else:
              font.setPointSize(QtGui.qApp.font().pointSize())
          font.setStyleHint(QtGui.QFont.TypeWriter)
          self._set_font(font)
  
      def change_font_size(self, delta):
          """Change the font size by the specified amount (in points).
          """
          font = self.font
          size = max(font.pointSize() + delta, 1) # minimum 1 point
          font.setPointSize(size)
          self._set_font(font)
  
      def _increase_font_size(self):
          self.change_font_size(1)
  
      def _decrease_font_size(self):
          self.change_font_size(-1)
  
      def select_all(self):
          """ Selects all the text in the buffer.
          """
          self._control.selectAll()
  
      def _get_tab_width(self):
          """ The width (in terms of space characters) for tab characters.
          """
          return self._tab_width
  
      def _set_tab_width(self, tab_width):
          """ Sets the width (in terms of space characters) for tab characters.
          """
          font_metrics = QtGui.QFontMetrics(self.font)
          self._control.setTabStopWidth(tab_width * font_metrics.width(' '))
  
          self._tab_width = tab_width
  
      tab_width = property(_get_tab_width, _set_tab_width)
  
      def undo(self):
          """ Undo the last operation. If there is no operation to undo, nothing
              happens.
          """
          self._control.undo()
  
      #---------------------------------------------------------------------------
      # 'ConsoleWidget' abstract interface
      #---------------------------------------------------------------------------
  
      def _is_complete(self, source, interactive):
          """ Returns whether 'source' can be executed. When triggered by an
              Enter/Return key press, 'interactive' is True; otherwise, it is
              False.
          """
          raise NotImplementedError
  
      def _execute(self, source, hidden):
          """ Execute 'source'. If 'hidden', do not show any output.
          """
          raise NotImplementedError
  
      def _prompt_started_hook(self):
          """ Called immediately after a new prompt is displayed.
          """
          pass
  
      def _prompt_finished_hook(self):
          """ Called immediately after a prompt is finished, i.e. when some input
              will be processed and a new prompt displayed.
          """
          pass
  
      def _up_pressed(self, shift_modifier):
          """ Called when the up key is pressed. Returns whether to continue
              processing the event.
          """
          return True
  
      def _down_pressed(self, shift_modifier):
          """ Called when the down key is pressed. Returns whether to continue
              processing the event.
          """
          return True
  
      def _tab_pressed(self):
          """ Called when the tab key is pressed. Returns whether to continue
              processing the event.
          """
          return False
  
      #--------------------------------------------------------------------------
      # 'ConsoleWidget' protected interface
      #--------------------------------------------------------------------------
  
      def _append_custom(self, insert, input, before_prompt=False, *args, **kwargs):
          """ A low-level method for appending content to the end of the buffer.
  
          If 'before_prompt' is enabled, the content will be inserted before the
          current prompt, if there is one.
          """
          # Determine where to insert the content.
          cursor = self._control.textCursor()
          if before_prompt and (self._reading or not self._executing):
              self._flush_pending_stream()
              cursor.setPosition(self._append_before_prompt_pos)
          else:
              if insert != self._insert_plain_text:
                  self._flush_pending_stream()
              cursor.movePosition(QtGui.QTextCursor.End)
          start_pos = cursor.position()
  
          # Perform the insertion.
          result = insert(cursor, input, *args, **kwargs)
  
          # Adjust the prompt position if we have inserted before it. This is safe
          # because buffer truncation is disabled when not executing.
          if before_prompt and (self._reading or not self._executing):
              diff = cursor.position() - start_pos
              self._append_before_prompt_pos += diff
              self._prompt_pos += diff
  
          return result
  
      def _append_block(self, block_format=None, before_prompt=False):
          """ Appends an new QTextBlock to the end of the console buffer.
          """
          self._append_custom(self._insert_block, block_format, before_prompt)
  
      def _append_html(self, html, before_prompt=False):
          """ Appends HTML at the end of the console buffer.
          """
          self._append_custom(self._insert_html, html, before_prompt)
  
      def _append_html_fetching_plain_text(self, html, before_prompt=False):
          """ Appends HTML, then returns the plain text version of it.
          """
          return self._append_custom(self._insert_html_fetching_plain_text,
                                     html, before_prompt)
  
      def _append_plain_text(self, text, before_prompt=False):
          """ Appends plain text, processing ANSI codes if enabled.
          """
          self._append_custom(self._insert_plain_text, text, before_prompt)
  
      def _cancel_completion(self):
          """ If text completion is progress, cancel it.
          """
          self._completion_widget.cancel_completion()
  
      def _clear_temporary_buffer(self):
          """ Clears the "temporary text" buffer, i.e. all the text following
              the prompt region.
          """
          # Select and remove all text below the input buffer.
          cursor = self._get_prompt_cursor()
          prompt = self._continuation_prompt.lstrip()
          if(self._temp_buffer_filled):
              self._temp_buffer_filled = False
              while cursor.movePosition(QtGui.QTextCursor.NextBlock):
                  temp_cursor = QtGui.QTextCursor(cursor)
                  temp_cursor.select(QtGui.QTextCursor.BlockUnderCursor)
                  text = temp_cursor.selection().toPlainText().lstrip()
                  if not text.startswith(prompt):
                      break
          else:
              # We've reached the end of the input buffer and no text follows.
              return
          cursor.movePosition(QtGui.QTextCursor.Left) # Grab the newline.
          cursor.movePosition(QtGui.QTextCursor.End,
                              QtGui.QTextCursor.KeepAnchor)
          cursor.removeSelectedText()
  
          # After doing this, we have no choice but to clear the undo/redo
          # history. Otherwise, the text is not "temporary" at all, because it
          # can be recalled with undo/redo. Unfortunately, Qt does not expose
          # fine-grained control to the undo/redo system.
          if self._control.isUndoRedoEnabled():
              self._control.setUndoRedoEnabled(False)
              self._control.setUndoRedoEnabled(True)
  
      def _complete_with_items(self, cursor, items):
          """ Performs completion with 'items' at the specified cursor location.
          """
          self._cancel_completion()
  
          if len(items) == 1:
              cursor.setPosition(self._control.textCursor().position(),
                                 QtGui.QTextCursor.KeepAnchor)
              cursor.insertText(items[0])
  
          elif len(items) > 1:
              current_pos = self._control.textCursor().position()
              prefix = os.path.commonprefix(items)
              if prefix:
                  cursor.setPosition(current_pos, QtGui.QTextCursor.KeepAnchor)
                  cursor.insertText(prefix)
                  current_pos = cursor.position()
  
              cursor.movePosition(QtGui.QTextCursor.Left, n=len(prefix))
              self._completion_widget.show_items(cursor, items)
  
  
      def _fill_temporary_buffer(self, cursor, text, html=False):
          """fill the area below the active editting zone with text"""
  
          current_pos = self._control.textCursor().position()
  
          cursor.beginEditBlock()
          self._append_plain_text('\n')
          self._page(text, html=html)
          cursor.endEditBlock()
  
          cursor.setPosition(current_pos)
          self._control.moveCursor(QtGui.QTextCursor.End)
          self._control.setTextCursor(cursor)
  
          self._temp_buffer_filled = True
  
  
      def _context_menu_make(self, pos):
          """ Creates a context menu for the given QPoint (in widget coordinates).
          """
          menu = QtGui.QMenu(self)
  
          self.cut_action = menu.addAction('Cut', self.cut)
          self.cut_action.setEnabled(self.can_cut())
          self.cut_action.setShortcut(QtGui.QKeySequence.Cut)
  
          self.copy_action = menu.addAction('Copy', self.copy)
          self.copy_action.setEnabled(self.can_copy())
          self.copy_action.setShortcut(QtGui.QKeySequence.Copy)
  
          self.paste_action = menu.addAction('Paste', self.paste)
          self.paste_action.setEnabled(self.can_paste())
          self.paste_action.setShortcut(QtGui.QKeySequence.Paste)
  
          anchor = self._control.anchorAt(pos)
          if anchor:
              menu.addSeparator()
              self.copy_link_action = menu.addAction(
                  'Copy Link Address', lambda: self.copy_anchor(anchor=anchor))
              self.open_link_action = menu.addAction(
                  'Open Link', lambda: self.open_anchor(anchor=anchor))
  
          menu.addSeparator()
          menu.addAction(self.select_all_action)
  
          menu.addSeparator()
          menu.addAction(self.export_action)
          menu.addAction(self.print_action)
  
          return menu
  
      def _control_key_down(self, modifiers, include_command=False):
          """ Given a KeyboardModifiers flags object, return whether the Control
          key is down.
  
          Parameters
          ----------
          include_command : bool, optional (default True)
              Whether to treat the Command key as a (mutually exclusive) synonym
              for Control when in Mac OS.
          """
          # Note that on Mac OS, ControlModifier corresponds to the Command key
          # while MetaModifier corresponds to the Control key.
          if sys.platform == 'darwin':
              down = include_command and (modifiers & QtCore.Qt.ControlModifier)
              return bool(down) ^ bool(modifiers & QtCore.Qt.MetaModifier)
          else:
              return bool(modifiers & QtCore.Qt.ControlModifier)
  
      def _create_control(self):
          """ Creates and connects the underlying text widget.
          """
          # Create the underlying control.
          if self.custom_control:
              control = self.custom_control()
          elif self.kind == 'plain':
              control = QtGui.QPlainTextEdit()
          elif self.kind == 'rich':
              control = QtGui.QTextEdit()
              control.setAcceptRichText(False)
              control.setMouseTracking(True)
  
          # Prevent the widget from handling drops, as we already provide
          # the logic in this class.
          control.setAcceptDrops(False)
  
          # Install event filters. The filter on the viewport is needed for
          # mouse events.
          control.installEventFilter(self)
          control.viewport().installEventFilter(self)
  
          # Connect signals.
          control.customContextMenuRequested.connect(
              self._custom_context_menu_requested)
          control.copyAvailable.connect(self.copy_available)
          control.redoAvailable.connect(self.redo_available)
          control.undoAvailable.connect(self.undo_available)
  
          # Hijack the document size change signal to prevent Qt from adjusting
          # the viewport's scrollbar. We are relying on an implementation detail
          # of Q(Plain)TextEdit here, which is potentially dangerous, but without
          # this functionality we cannot create a nice terminal interface.
          layout = control.document().documentLayout()
          layout.documentSizeChanged.disconnect()
          layout.documentSizeChanged.connect(self._adjust_scrollbars)
  
          # Configure the control.
          control.setAttribute(QtCore.Qt.WA_InputMethodEnabled, True)
          control.setContextMenuPolicy(QtCore.Qt.CustomContextMenu)
          control.setReadOnly(True)
          control.setUndoRedoEnabled(False)
          control.setVerticalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOn)
          return control
  
      def _create_page_control(self):
          """ Creates and connects the underlying paging widget.
          """
          if self.custom_page_control:
              control = self.custom_page_control()
          elif self.kind == 'plain':
              control = QtGui.QPlainTextEdit()
          elif self.kind == 'rich':
              control = QtGui.QTextEdit()
          control.installEventFilter(self)
          viewport = control.viewport()
          viewport.installEventFilter(self)
          control.setReadOnly(True)
          control.setUndoRedoEnabled(False)
          control.setVerticalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOn)
          return control
  
      def _event_filter_console_keypress(self, event):
          """ Filter key events for the underlying text widget to create a
              console-like interface.
          """
          intercepted = False
          cursor = self._control.textCursor()
          position = cursor.position()
          key = event.key()
          ctrl_down = self._control_key_down(event.modifiers())
          alt_down = event.modifiers() & QtCore.Qt.AltModifier
          shift_down = event.modifiers() & QtCore.Qt.ShiftModifier
  
          #------ Special sequences ----------------------------------------------
  
          if event.matches(QtGui.QKeySequence.Copy):
              self.copy()
              intercepted = True
  
          elif event.matches(QtGui.QKeySequence.Cut):
              self.cut()
              intercepted = True
  
          elif event.matches(QtGui.QKeySequence.Paste):
              self.paste()
              intercepted = True
  
          #------ Special modifier logic -----------------------------------------
  
          elif key in (QtCore.Qt.Key_Return, QtCore.Qt.Key_Enter):
              intercepted = True
  
              # Special handling when tab completing in text mode.
              self._cancel_completion()
  
              if self._in_buffer(position):
                  # Special handling when a reading a line of raw input.
                  if self._reading:
                      self._append_plain_text('\n')
                      self._reading = False
                      if self._reading_callback:
                          self._reading_callback()
  
                  # If the input buffer is a single line or there is only
                  # whitespace after the cursor, execute. Otherwise, split the
                  # line with a continuation prompt.
                  elif not self._executing:
                      cursor.movePosition(QtGui.QTextCursor.End,
                                          QtGui.QTextCursor.KeepAnchor)
                      at_end = len(cursor.selectedText().strip()) == 0
                      single_line = (self._get_end_cursor().blockNumber() ==
                                     self._get_prompt_cursor().blockNumber())
                      if (at_end or shift_down or single_line) and not ctrl_down:
                          self.execute(interactive = not shift_down)
                      else:
                          # Do this inside an edit block for clean undo/redo.
                          cursor.beginEditBlock()
                          cursor.setPosition(position)
                          cursor.insertText('\n')
                          self._insert_continuation_prompt(cursor)
                          cursor.endEditBlock()
  
                          # Ensure that the whole input buffer is visible.
                          # FIXME: This will not be usable if the input buffer is
                          # taller than the console widget.
                          self._control.moveCursor(QtGui.QTextCursor.End)
                          self._control.setTextCursor(cursor)
  
          #------ Control/Cmd modifier -------------------------------------------
  
          elif ctrl_down:
              if key == QtCore.Qt.Key_G:
                  self._keyboard_quit()
                  intercepted = True
  
              elif key == QtCore.Qt.Key_K:
                  if self._in_buffer(position):
                      cursor.clearSelection()
                      cursor.movePosition(QtGui.QTextCursor.EndOfLine,
                                          QtGui.QTextCursor.KeepAnchor)
                      if not cursor.hasSelection():
                          # Line deletion (remove continuation prompt)
                          cursor.movePosition(QtGui.QTextCursor.NextBlock,
                                              QtGui.QTextCursor.KeepAnchor)
                          cursor.movePosition(QtGui.QTextCursor.Right,
                                              QtGui.QTextCursor.KeepAnchor,
                                              len(self._continuation_prompt))
                      self._kill_ring.kill_cursor(cursor)
                      self._set_cursor(cursor)
                  intercepted = True
  
              elif key == QtCore.Qt.Key_L:
                  self.prompt_to_top()
                  intercepted = True
  
              elif key == QtCore.Qt.Key_O:
                  if self._page_control and self._page_control.isVisible():
                      self._page_control.setFocus()
                  intercepted = True
  
              elif key == QtCore.Qt.Key_U:
                  if self._in_buffer(position):
                      cursor.clearSelection()
                      start_line = cursor.blockNumber()
                      if start_line == self._get_prompt_cursor().blockNumber():
                          offset = len(self._prompt)
                      else:
                          offset = len(self._continuation_prompt)
                      cursor.movePosition(QtGui.QTextCursor.StartOfBlock,
                                          QtGui.QTextCursor.KeepAnchor)
                      cursor.movePosition(QtGui.QTextCursor.Right,
                                          QtGui.QTextCursor.KeepAnchor, offset)
                      self._kill_ring.kill_cursor(cursor)
                      self._set_cursor(cursor)
                  intercepted = True
  
              elif key == QtCore.Qt.Key_Y:
                  self._keep_cursor_in_buffer()
                  self._kill_ring.yank()
                  intercepted = True
  
              elif key in (QtCore.Qt.Key_Backspace, QtCore.Qt.Key_Delete):
                  if key == QtCore.Qt.Key_Backspace:
                      cursor = self._get_word_start_cursor(position)
                  else: # key == QtCore.Qt.Key_Delete
                      cursor = self._get_word_end_cursor(position)
                  cursor.setPosition(position, QtGui.QTextCursor.KeepAnchor)
                  self._kill_ring.kill_cursor(cursor)
                  intercepted = True
  
              elif key == QtCore.Qt.Key_D:
                  if len(self.input_buffer) == 0:
                      self.exit_requested.emit(self)
                  else:
                      new_event = QtGui.QKeyEvent(QtCore.QEvent.KeyPress,
                                                  QtCore.Qt.Key_Delete,
                                                  QtCore.Qt.NoModifier)
                      QtGui.qApp.sendEvent(self._control, new_event)
                      intercepted = True
  
          #------ Alt modifier ---------------------------------------------------
  
          elif alt_down:
              if key == QtCore.Qt.Key_B:
                  self._set_cursor(self._get_word_start_cursor(position))
                  intercepted = True
  
              elif key == QtCore.Qt.Key_F:
                  self._set_cursor(self._get_word_end_cursor(position))
                  intercepted = True
  
              elif key == QtCore.Qt.Key_Y:
                  self._kill_ring.rotate()
                  intercepted = True
  
              elif key == QtCore.Qt.Key_Backspace:
                  cursor = self._get_word_start_cursor(position)
                  cursor.setPosition(position, QtGui.QTextCursor.KeepAnchor)
                  self._kill_ring.kill_cursor(cursor)
                  intercepted = True
  
              elif key == QtCore.Qt.Key_D:
                  cursor = self._get_word_end_cursor(position)
                  cursor.setPosition(position, QtGui.QTextCursor.KeepAnchor)
                  self._kill_ring.kill_cursor(cursor)
                  intercepted = True
  
              elif key == QtCore.Qt.Key_Delete:
                  intercepted = True
  
              elif key == QtCore.Qt.Key_Greater:
                  self._control.moveCursor(QtGui.QTextCursor.End)
                  intercepted = True
  
              elif key == QtCore.Qt.Key_Less:
                  self._control.setTextCursor(self._get_prompt_cursor())
                  intercepted = True
  
          #------ No modifiers ---------------------------------------------------
  
          else:
              if shift_down:
                  anchormode = QtGui.QTextCursor.KeepAnchor
              else:
                  anchormode = QtGui.QTextCursor.MoveAnchor
  
              if key == QtCore.Qt.Key_Escape:
                  self._keyboard_quit()
                  intercepted = True
  
              elif key == QtCore.Qt.Key_Up:
                  if self._reading or not self._up_pressed(shift_down):
                      intercepted = True
                  else:
                      prompt_line = self._get_prompt_cursor().blockNumber()
                      intercepted = cursor.blockNumber() <= prompt_line
  
              elif key == QtCore.Qt.Key_Down:
                  if self._reading or not self._down_pressed(shift_down):
                      intercepted = True
                  else:
                      end_line = self._get_end_cursor().blockNumber()
                      intercepted = cursor.blockNumber() == end_line
  
              elif key == QtCore.Qt.Key_Tab:
                  if not self._reading:
                      if self._tab_pressed():
                          # real tab-key, insert four spaces
                          cursor.insertText(' '*4)
                      intercepted = True
  
              elif key == QtCore.Qt.Key_Left:
  
                  # Move to the previous line
                  line, col = cursor.blockNumber(), cursor.columnNumber()
                  if line > self._get_prompt_cursor().blockNumber() and \
                          col == len(self._continuation_prompt):
                      self._control.moveCursor(QtGui.QTextCursor.PreviousBlock,
                                               mode=anchormode)
                      self._control.moveCursor(QtGui.QTextCursor.EndOfBlock,
                                               mode=anchormode)
                      intercepted = True
  
                  # Regular left movement
                  else:
                      intercepted = not self._in_buffer(position - 1)
  
              elif key == QtCore.Qt.Key_Right:
                  original_block_number = cursor.blockNumber()
                  self._control.moveCursor(QtGui.QTextCursor.Right,
                                  mode=anchormode)
                  if cursor.blockNumber() != original_block_number:
                      self._control.moveCursor(QtGui.QTextCursor.Right,
                                          n=len(self._continuation_prompt),
                                          mode=anchormode)
                  intercepted = True
  
              elif key == QtCore.Qt.Key_Home:
                  start_line = cursor.blockNumber()
                  if start_line == self._get_prompt_cursor().blockNumber():
                      start_pos = self._prompt_pos
                  else:
                      cursor.movePosition(QtGui.QTextCursor.StartOfBlock,
                                          QtGui.QTextCursor.KeepAnchor)
                      start_pos = cursor.position()
                      start_pos += len(self._continuation_prompt)
                      cursor.setPosition(position)
                  if shift_down and self._in_buffer(position):
                      cursor.setPosition(start_pos, QtGui.QTextCursor.KeepAnchor)
                  else:
                      cursor.setPosition(start_pos)
                  self._set_cursor(cursor)
                  intercepted = True
  
              elif key == QtCore.Qt.Key_Backspace:
  
                  # Line deletion (remove continuation prompt)
                  line, col = cursor.blockNumber(), cursor.columnNumber()
                  if not self._reading and \
                          col == len(self._continuation_prompt) and \
                          line > self._get_prompt_cursor().blockNumber():
                      cursor.beginEditBlock()
                      cursor.movePosition(QtGui.QTextCursor.StartOfBlock,
                                          QtGui.QTextCursor.KeepAnchor)
                      cursor.removeSelectedText()
                      cursor.deletePreviousChar()
                      cursor.endEditBlock()
                      intercepted = True
  
                  # Regular backwards deletion
                  else:
                      anchor = cursor.anchor()
                      if anchor == position:
                          intercepted = not self._in_buffer(position - 1)
                      else:
                          intercepted = not self._in_buffer(min(anchor, position))
  
              elif key == QtCore.Qt.Key_Delete:
  
                  # Line deletion (remove continuation prompt)
                  if not self._reading and self._in_buffer(position) and \
                          cursor.atBlockEnd() and not cursor.hasSelection():
                      cursor.movePosition(QtGui.QTextCursor.NextBlock,
                                          QtGui.QTextCursor.KeepAnchor)
                      cursor.movePosition(QtGui.QTextCursor.Right,
                                          QtGui.QTextCursor.KeepAnchor,
                                          len(self._continuation_prompt))
                      cursor.removeSelectedText()
                      intercepted = True
  
                  # Regular forwards deletion:
                  else:
                      anchor = cursor.anchor()
                      intercepted = (not self._in_buffer(anchor) or
                                     not self._in_buffer(position))
  
          # Don't move the cursor if Control/Cmd is pressed to allow copy-paste
          # using the keyboard in any part of the buffer. Also, permit scrolling
          # with Page Up/Down keys. Finally, if we're executing, don't move the
          # cursor (if even this made sense, we can't guarantee that the prompt
          # position is still valid due to text truncation).
          if not (self._control_key_down(event.modifiers(), include_command=True)
                  or key in (QtCore.Qt.Key_PageUp, QtCore.Qt.Key_PageDown)
                  or (self._executing and not self._reading)):
              self._keep_cursor_in_buffer()
  
          return intercepted
  
      def _event_filter_page_keypress(self, event):
          """ Filter key events for the paging widget to create console-like
              interface.
          """
          key = event.key()
          ctrl_down = self._control_key_down(event.modifiers())
          alt_down = event.modifiers() & QtCore.Qt.AltModifier
  
          if ctrl_down:
              if key == QtCore.Qt.Key_O:
                  self._control.setFocus()
                  intercept = True
  
          elif alt_down:
              if key == QtCore.Qt.Key_Greater:
                  self._page_control.moveCursor(QtGui.QTextCursor.End)
                  intercepted = True
  
              elif key == QtCore.Qt.Key_Less:
                  self._page_control.moveCursor(QtGui.QTextCursor.Start)
                  intercepted = True
  
          elif key in (QtCore.Qt.Key_Q, QtCore.Qt.Key_Escape):
              if self._splitter:
                  self._page_control.hide()
                  self._control.setFocus()
              else:
                  self.layout().setCurrentWidget(self._control)
                  # re-enable buffer truncation after paging
                  self._control.document().setMaximumBlockCount(self.buffer_size)
              return True
  
          elif key in (QtCore.Qt.Key_Enter, QtCore.Qt.Key_Return,
                       QtCore.Qt.Key_Tab):
              new_event = QtGui.QKeyEvent(QtCore.QEvent.KeyPress,
                                          QtCore.Qt.Key_PageDown,
                                          QtCore.Qt.NoModifier)
              QtGui.qApp.sendEvent(self._page_control, new_event)
              return True
  
          elif key == QtCore.Qt.Key_Backspace:
              new_event = QtGui.QKeyEvent(QtCore.QEvent.KeyPress,
                                          QtCore.Qt.Key_PageUp,
                                          QtCore.Qt.NoModifier)
              QtGui.qApp.sendEvent(self._page_control, new_event)
              return True
  
          # vi/less -like key bindings
          elif key == QtCore.Qt.Key_J:
              new_event = QtGui.QKeyEvent(QtCore.QEvent.KeyPress,
                                          QtCore.Qt.Key_Down,
                                          QtCore.Qt.NoModifier)
              QtGui.qApp.sendEvent(self._page_control, new_event)
              return True
  
          # vi/less -like key bindings
          elif key == QtCore.Qt.Key_K:
              new_event = QtGui.QKeyEvent(QtCore.QEvent.KeyPress,
                                          QtCore.Qt.Key_Up,
                                          QtCore.Qt.NoModifier)
              QtGui.qApp.sendEvent(self._page_control, new_event)
              return True
  
          return False
  
      def _on_flush_pending_stream_timer(self):
          """ Flush the pending stream output and change the
          prompt position appropriately.
          """
          cursor = self._control.textCursor()
          cursor.movePosition(QtGui.QTextCursor.End)
          pos = cursor.position()
          self._flush_pending_stream()
          cursor.movePosition(QtGui.QTextCursor.End)
          diff = cursor.position() - pos
          if diff > 0:
              self._prompt_pos += diff
              self._append_before_prompt_pos += diff
  
      def _flush_pending_stream(self):
          """ Flush out pending text into the widget. """
          text = self._pending_insert_text
          self._pending_insert_text = []
          buffer_size = self._control.document().maximumBlockCount()
          if buffer_size > 0:
              text = self._get_last_lines_from_list(text, buffer_size)
          text = ''.join(text)
          t = time.time()
          self._insert_plain_text(self._get_end_cursor(), text, flush=True)
          # Set the flush interval to equal the maximum time to update text.
          self._pending_text_flush_interval.setInterval(max(100,
                                                   (time.time()-t)*1000))
  
      def _format_as_columns(self, items, separator='  '):
          """ Transform a list of strings into a single string with columns.
  
          Parameters
          ----------
          items : sequence of strings
              The strings to process.
  
          separator : str, optional [default is two spaces]
              The string that separates columns.
  
          Returns
          -------
          The formatted string.
          """
          # Calculate the number of characters available.
          width = self._control.document().textWidth()
          char_width = QtGui.QFontMetrics(self.font).width(' ')
          displaywidth = max(10, (width / char_width) - 1)
  
          return columnize(items, separator, displaywidth)
  
      def _get_block_plain_text(self, block):
          """ Given a QTextBlock, return its unformatted text.
          """
          cursor = QtGui.QTextCursor(block)
          cursor.movePosition(QtGui.QTextCursor.StartOfBlock)
          cursor.movePosition(QtGui.QTextCursor.EndOfBlock,
                              QtGui.QTextCursor.KeepAnchor)
          return cursor.selection().toPlainText()
  
      def _get_cursor(self):
          """ Convenience method that returns a cursor for the current position.
          """
          return self._control.textCursor()
  
      def _get_end_cursor(self):
          """ Convenience method that returns a cursor for the last character.
          """
          cursor = self._control.textCursor()
          cursor.movePosition(QtGui.QTextCursor.End)
          return cursor
  
      def _get_input_buffer_cursor_column(self):
          """ Returns the column of the cursor in the input buffer, excluding the
              contribution by the prompt, or -1 if there is no such column.
          """
          prompt = self._get_input_buffer_cursor_prompt()
          if prompt is None:
              return -1
          else:
              cursor = self._control.textCursor()
              return cursor.columnNumber() - len(prompt)
  
      def _get_input_buffer_cursor_line(self):
          """ Returns the text of the line of the input buffer that contains the
              cursor, or None if there is no such line.
          """
          prompt = self._get_input_buffer_cursor_prompt()
          if prompt is None:
              return None
          else:
              cursor = self._control.textCursor()
              text = self._get_block_plain_text(cursor.block())
              return text[len(prompt):]
      
      def _get_input_buffer_cursor_pos(self):
          """Return the cursor position within the input buffer."""
          cursor = self._control.textCursor()
          cursor.setPosition(self._prompt_pos, QtGui.QTextCursor.KeepAnchor)
          input_buffer = cursor.selection().toPlainText()
          
          # Don't count continuation prompts
          return len(input_buffer.replace('\n' + self._continuation_prompt, '\n'))
      
      def _get_input_buffer_cursor_prompt(self):
          """ Returns the (plain text) prompt for line of the input buffer that
              contains the cursor, or None if there is no such line.
          """
          if self._executing:
              return None
          cursor = self._control.textCursor()
          if cursor.position() >= self._prompt_pos:
              if cursor.blockNumber() == self._get_prompt_cursor().blockNumber():
                  return self._prompt
              else:
                  return self._continuation_prompt
          else:
              return None
  
      def _get_last_lines(self, text, num_lines, return_count=False):
          """ Return last specified number of lines of text (like `tail -n`).
          If return_count is True, returns a tuple of clipped text and the
          number of lines in the clipped text.
          """
          pos = len(text)
          if pos < num_lines:
              if return_count:
                  return text, text.count('\n') if return_count else text
              else:
                  return text
          i = 0
          while i < num_lines:
              pos = text.rfind('\n', None, pos)
              if pos == -1:
                  pos = None
                  break
              i += 1
          if return_count:
              return text[pos:], i
          else:
              return text[pos:]
  
      def _get_last_lines_from_list(self, text_list, num_lines):
          """ Return the list of text clipped to last specified lines.
          """
          ret = []
          lines_pending = num_lines
          for text in reversed(text_list):
              text, lines_added = self._get_last_lines(text, lines_pending,
                                                       return_count=True)
              ret.append(text)
              lines_pending -= lines_added
              if lines_pending <= 0:
                  break
          return ret[::-1]
  
      def _get_prompt_cursor(self):
          """ Convenience method that returns a cursor for the prompt position.
          """
          cursor = self._control.textCursor()
          cursor.setPosition(self._prompt_pos)
          return cursor
  
      def _get_selection_cursor(self, start, end):
          """ Convenience method that returns a cursor with text selected between
              the positions 'start' and 'end'.
          """
          cursor = self._control.textCursor()
          cursor.setPosition(start)
          cursor.setPosition(end, QtGui.QTextCursor.KeepAnchor)
          return cursor
  
      def _get_word_start_cursor(self, position):
          """ Find the start of the word to the left the given position. If a
              sequence of non-word characters precedes the first word, skip over
              them. (This emulates the behavior of bash, emacs, etc.)
          """
          document = self._control.document()
          position -= 1
          while position >= self._prompt_pos and \
                    not is_letter_or_number(document.characterAt(position)):
              position -= 1
          while position >= self._prompt_pos and \
                    is_letter_or_number(document.characterAt(position)):
              position -= 1
          cursor = self._control.textCursor()
          cursor.setPosition(position + 1)
          return cursor
  
      def _get_word_end_cursor(self, position):
          """ Find the end of the word to the right the given position. If a
              sequence of non-word characters precedes the first word, skip over
              them. (This emulates the behavior of bash, emacs, etc.)
          """
          document = self._control.document()
          end = self._get_end_cursor().position()
          while position < end and \
                    not is_letter_or_number(document.characterAt(position)):
              position += 1
          while position < end and \
                    is_letter_or_number(document.characterAt(position)):
              position += 1
          cursor = self._control.textCursor()
          cursor.setPosition(position)
          return cursor
  
      def _insert_continuation_prompt(self, cursor):
          """ Inserts new continuation prompt using the specified cursor.
          """
          if self._continuation_prompt_html is None:
              self._insert_plain_text(cursor, self._continuation_prompt)
          else:
              self._continuation_prompt = self._insert_html_fetching_plain_text(
                  cursor, self._continuation_prompt_html)
  
      def _insert_block(self, cursor, block_format=None):
          """ Inserts an empty QTextBlock using the specified cursor.
          """
          if block_format is None:
              block_format = QtGui.QTextBlockFormat()
          cursor.insertBlock(block_format)
  
      def _insert_html(self, cursor, html):
          """ Inserts HTML using the specified cursor in such a way that future
              formatting is unaffected.
          """
          cursor.beginEditBlock()
          cursor.insertHtml(html)
  
          # After inserting HTML, the text document "remembers" it's in "html
          # mode", which means that subsequent calls adding plain text will result
          # in unwanted formatting, lost tab characters, etc. The following code
          # hacks around this behavior, which I consider to be a bug in Qt, by
          # (crudely) resetting the document's style state.
          cursor.movePosition(QtGui.QTextCursor.Left,
                              QtGui.QTextCursor.KeepAnchor)
          if cursor.selection().toPlainText() == ' ':
              cursor.removeSelectedText()
          else:
              cursor.movePosition(QtGui.QTextCursor.Right)
          cursor.insertText(' ', QtGui.QTextCharFormat())
          cursor.endEditBlock()
  
      def _insert_html_fetching_plain_text(self, cursor, html):
          """ Inserts HTML using the specified cursor, then returns its plain text
              version.
          """
          cursor.beginEditBlock()
          cursor.removeSelectedText()
  
          start = cursor.position()
          self._insert_html(cursor, html)
          end = cursor.position()
          cursor.setPosition(start, QtGui.QTextCursor.KeepAnchor)
          text = cursor.selection().toPlainText()
  
          cursor.setPosition(end)
          cursor.endEditBlock()
          return text
  
      def _insert_plain_text(self, cursor, text, flush=False):
          """ Inserts plain text using the specified cursor, processing ANSI codes
              if enabled.
          """
          # maximumBlockCount() can be different from self.buffer_size in
          # case input prompt is active.
          buffer_size = self._control.document().maximumBlockCount()
  
          if (self._executing and not flush and
                  self._pending_text_flush_interval.isActive() and
                  cursor.position() == self._get_end_cursor().position()):
              # Queue the text to insert in case it is being inserted at end
              self._pending_insert_text.append(text)
              if buffer_size > 0:
                  self._pending_insert_text = self._get_last_lines_from_list(
                                          self._pending_insert_text, buffer_size)
              return
  
          if self._executing and not self._pending_text_flush_interval.isActive():
              self._pending_text_flush_interval.start()
  
          # Clip the text to last `buffer_size` lines.
          if buffer_size > 0:
              text = self._get_last_lines(text, buffer_size)
  
          cursor.beginEditBlock()
          if self.ansi_codes:
              for substring in self._ansi_processor.split_string(text):
                  for act in self._ansi_processor.actions:
  
                      # Unlike real terminal emulators, we don't distinguish
                      # between the screen and the scrollback buffer. A screen
                      # erase request clears everything.
                      if act.action == 'erase' and act.area == 'screen':
                          cursor.select(QtGui.QTextCursor.Document)
                          cursor.removeSelectedText()
  
                      # Simulate a form feed by scrolling just past the last line.
                      elif act.action == 'scroll' and act.unit == 'page':
                          cursor.insertText('\n')
                          cursor.endEditBlock()
                          self._set_top_cursor(cursor)
                          cursor.joinPreviousEditBlock()
                          cursor.deletePreviousChar()
  
                      elif act.action == 'carriage-return':
                          cursor.movePosition(
                              cursor.StartOfLine, cursor.KeepAnchor)
  
                      elif act.action == 'beep':
                          QtGui.qApp.beep()
  
                      elif act.action == 'backspace':
                          if not cursor.atBlockStart():
                              cursor.movePosition(
                                  cursor.PreviousCharacter, cursor.KeepAnchor)
  
                      elif act.action == 'newline':
                          cursor.movePosition(cursor.EndOfLine)
  
                  format = self._ansi_processor.get_format()
  
                  selection = cursor.selectedText()
                  if len(selection) == 0:
                      cursor.insertText(substring, format)
                  elif substring is not None:
                      # BS and CR are treated as a change in print
                      # position, rather than a backwards character
                      # deletion for output equivalence with (I)Python
                      # terminal.
                      if len(substring) >= len(selection):
                          cursor.insertText(substring, format)
                      else:
                          old_text = selection[len(substring):]
                          cursor.insertText(substring + old_text, format)
                          cursor.movePosition(cursor.PreviousCharacter,
                                 cursor.KeepAnchor, len(old_text))
          else:
              cursor.insertText(text)
          cursor.endEditBlock()
  
      def _insert_plain_text_into_buffer(self, cursor, text):
          """ Inserts text into the input buffer using the specified cursor (which
              must be in the input buffer), ensuring that continuation prompts are
              inserted as necessary.
          """
          lines = text.splitlines(True)
          if lines:
              if lines[-1].endswith('\n'):
                  # If the text ends with a newline, add a blank line so a new
                  # continuation prompt is produced.
                  lines.append('')
              cursor.beginEditBlock()
              cursor.insertText(lines[0])
              for line in lines[1:]:
                  if self._continuation_prompt_html is None:
                      cursor.insertText(self._continuation_prompt)
                  else:
                      self._continuation_prompt = \
                          self._insert_html_fetching_plain_text(
                              cursor, self._continuation_prompt_html)
                  cursor.insertText(line)
              cursor.endEditBlock()
  
      def _in_buffer(self, position=None):
          """ Returns whether the current cursor (or, if specified, a position) is
              inside the editing region.
          """
          cursor = self._control.textCursor()
          if position is None:
              position = cursor.position()
          else:
              cursor.setPosition(position)
          line = cursor.blockNumber()
          prompt_line = self._get_prompt_cursor().blockNumber()
          if line == prompt_line:
              return position >= self._prompt_pos
          elif line > prompt_line:
              cursor.movePosition(QtGui.QTextCursor.StartOfBlock)
              prompt_pos = cursor.position() + len(self._continuation_prompt)
              return position >= prompt_pos
          return False
  
      def _keep_cursor_in_buffer(self):
          """ Ensures that the cursor is inside the editing region. Returns
              whether the cursor was moved.
          """
          moved = not self._in_buffer()
          if moved:
              cursor = self._control.textCursor()
              cursor.movePosition(QtGui.QTextCursor.End)
              self._control.setTextCursor(cursor)
          return moved
  
      def _keyboard_quit(self):
          """ Cancels the current editing task ala Ctrl-G in Emacs.
          """
          if self._temp_buffer_filled :
              self._cancel_completion()
              self._clear_temporary_buffer()
          else:
              self.input_buffer = ''
  
      def _page(self, text, html=False):
          """ Displays text using the pager if it exceeds the height of the
          viewport.
  
          Parameters
          ----------
          html : bool, optional (default False)
              If set, the text will be interpreted as HTML instead of plain text.
          """
          line_height = QtGui.QFontMetrics(self.font).height()
          minlines = self._control.viewport().height() / line_height
          if self.paging != 'none' and \
                  re.match("(?:[^\n]*\n){%i}" % minlines, text):
              if self.paging == 'custom':
                  self.custom_page_requested.emit(text)
              else:
                  # disable buffer truncation during paging
                  self._control.document().setMaximumBlockCount(0)
                  self._page_control.clear()
                  cursor = self._page_control.textCursor()
                  if html:
                      self._insert_html(cursor, text)
                  else:
                      self._insert_plain_text(cursor, text)
                  self._page_control.moveCursor(QtGui.QTextCursor.Start)
  
                  self._page_control.viewport().resize(self._control.size())
                  if self._splitter:
                      self._page_control.show()
                      self._page_control.setFocus()
                  else:
                      self.layout().setCurrentWidget(self._page_control)
          elif html:
              self._append_html(text)
          else:
              self._append_plain_text(text)
  
      def _set_paging(self, paging):
          """
          Change the pager to `paging` style.
  
          Parameters
          ----------
          paging : string
              Either "hsplit", "vsplit", or "inside"
          """
          if self._splitter is None:
              raise NotImplementedError("""can only switch if --paging=hsplit or
                      --paging=vsplit is used.""")
          if paging == 'hsplit':
              self._splitter.setOrientation(QtCore.Qt.Horizontal)
          elif paging == 'vsplit':
              self._splitter.setOrientation(QtCore.Qt.Vertical)
          elif paging == 'inside':
              raise NotImplementedError("""switching to 'inside' paging not
                      supported yet.""")
          else:
              raise ValueError("unknown paging method '%s'" % paging)
          self.paging = paging
  
      def _prompt_finished(self):
          """ Called immediately after a prompt is finished, i.e. when some input
              will be processed and a new prompt displayed.
          """
          self._control.setReadOnly(True)
          self._prompt_finished_hook()
  
      def _prompt_started(self):
          """ Called immediately after a new prompt is displayed.
          """
          # Temporarily disable the maximum block count to permit undo/redo and
          # to ensure that the prompt position does not change due to truncation.
          self._control.document().setMaximumBlockCount(0)
          self._control.setUndoRedoEnabled(True)
  
          # Work around bug in QPlainTextEdit: input method is not re-enabled
          # when read-only is disabled.
          self._control.setReadOnly(False)
          self._control.setAttribute(QtCore.Qt.WA_InputMethodEnabled, True)
  
          if not self._reading:
              self._executing = False
          self._prompt_started_hook()
  
          # If the input buffer has changed while executing, load it.
          if self._input_buffer_pending:
              self.input_buffer = self._input_buffer_pending
              self._input_buffer_pending = ''
  
          self._control.moveCursor(QtGui.QTextCursor.End)
  
      def _readline(self, prompt='', callback=None, password=False):
          """ Reads one line of input from the user.
  
          Parameters
          ----------
          prompt : str, optional
              The prompt to print before reading the line.
  
          callback : callable, optional
              A callback to execute with the read line. If not specified, input is
              read *synchronously* and this method does not return until it has
              been read.
  
          Returns
          -------
          If a callback is specified, returns nothing. Otherwise, returns the
          input string with the trailing newline stripped.
          """
          if self._reading:
              raise RuntimeError('Cannot read a line. Widget is already reading.')
  
          if not callback and not self.isVisible():
              # If the user cannot see the widget, this function cannot return.
              raise RuntimeError('Cannot synchronously read a line if the widget '
                                 'is not visible!')
  
          self._reading = True
          if password:
              self._show_prompt('Warning: QtConsole does not support password mode, '\
                                'the text you type will be visible.', newline=True)
          self._show_prompt(prompt, newline=False)
  
          if callback is None:
              self._reading_callback = None
              while self._reading:
                  QtCore.QCoreApplication.processEvents()
              return self._get_input_buffer(force=True).rstrip('\n')
  
          else:
              self._reading_callback = lambda: \
                  callback(self._get_input_buffer(force=True).rstrip('\n'))
  
      def _set_continuation_prompt(self, prompt, html=False):
          """ Sets the continuation prompt.
  
          Parameters
          ----------
          prompt : str
              The prompt to show when more input is needed.
  
          html : bool, optional (default False)
              If set, the prompt will be inserted as formatted HTML. Otherwise,
              the prompt will be treated as plain text, though ANSI color codes
              will be handled.
          """
          if html:
              self._continuation_prompt_html = prompt
          else:
              self._continuation_prompt = prompt
              self._continuation_prompt_html = None
  
      def _set_cursor(self, cursor):
          """ Convenience method to set the current cursor.
          """
          self._control.setTextCursor(cursor)
  
      def _set_top_cursor(self, cursor):
          """ Scrolls the viewport so that the specified cursor is at the top.
          """
          scrollbar = self._control.verticalScrollBar()
          scrollbar.setValue(scrollbar.maximum())
          original_cursor = self._control.textCursor()
          self._control.setTextCursor(cursor)
          self._control.ensureCursorVisible()
          self._control.setTextCursor(original_cursor)
  
      def _show_prompt(self, prompt=None, html=False, newline=True):
          """ Writes a new prompt at the end of the buffer.
  
          Parameters
          ----------
          prompt : str, optional
              The prompt to show. If not specified, the previous prompt is used.
  
          html : bool, optional (default False)
              Only relevant when a prompt is specified. If set, the prompt will
              be inserted as formatted HTML. Otherwise, the prompt will be treated
              as plain text, though ANSI color codes will be handled.
  
          newline : bool, optional (default True)
              If set, a new line will be written before showing the prompt if
              there is not already a newline at the end of the buffer.
          """
          # Save the current end position to support _append*(before_prompt=True).
          self._flush_pending_stream()
          cursor = self._get_end_cursor()
          self._append_before_prompt_pos = cursor.position()
  
          # Insert a preliminary newline, if necessary.
          if newline and cursor.position() > 0:
              cursor.movePosition(QtGui.QTextCursor.Left,
                                  QtGui.QTextCursor.KeepAnchor)
              if cursor.selection().toPlainText() != '\n':
                  self._append_block()
                  self._append_before_prompt_pos += 1
  
          # Write the prompt.
          self._append_plain_text(self._prompt_sep)
          if prompt is None:
              if self._prompt_html is None:
                  self._append_plain_text(self._prompt)
              else:
                  self._append_html(self._prompt_html)
          else:
              if html:
                  self._prompt = self._append_html_fetching_plain_text(prompt)
                  self._prompt_html = prompt
              else:
                  self._append_plain_text(prompt)
                  self._prompt = prompt
                  self._prompt_html = None
  
          self._flush_pending_stream()
          self._prompt_pos = self._get_end_cursor().position()
          self._prompt_started()
  
      #------ Signal handlers ----------------------------------------------------
  
      def _adjust_scrollbars(self):
          """ Expands the vertical scrollbar beyond the range set by Qt.
          """
          # This code is adapted from _q_adjustScrollbars in qplaintextedit.cpp
          # and qtextedit.cpp.
          document = self._control.document()
          scrollbar = self._control.verticalScrollBar()
          viewport_height = self._control.viewport().height()
          if isinstance(self._control, QtGui.QPlainTextEdit):
              maximum = max(0, document.lineCount() - 1)
              step = viewport_height / self._control.fontMetrics().lineSpacing()
          else:
              # QTextEdit does not do line-based layout and blocks will not in
              # general have the same height. Therefore it does not make sense to
              # attempt to scroll in line height increments.
              maximum = document.size().height()
              step = viewport_height
          diff = maximum - scrollbar.maximum()
          scrollbar.setRange(0, maximum)
          scrollbar.setPageStep(step)
  
          # Compensate for undesirable scrolling that occurs automatically due to
          # maximumBlockCount() text truncation.
          if diff < 0 and document.blockCount() == document.maximumBlockCount():
              scrollbar.setValue(scrollbar.value() + diff)
  
      def _custom_context_menu_requested(self, pos):
          """ Shows a context menu at the given QPoint (in widget coordinates).
          """
          menu = self._context_menu_make(pos)
          menu.exec_(self._control.mapToGlobal(pos))
  