Clearing the ConsoleWidget now cancels reading, which is the intuitive behavior.

IPython/frontend/qt/console/console_widget.py

@@ -1,890 +1,892 b''
 # Standard library imports
 import re
 import sys
 
 # System library imports
 from PyQt4 import QtCore, QtGui
 
 # Local imports
 from completion_widget import CompletionWidget
 
 
 class AnsiCodeProcessor(object):
     """ Translates ANSI escape codes into readable attributes.
     """
 
     def __init__(self):
         self.ansi_colors = ( # Normal, Bright/Light
                              ('#000000', '#7f7f7f'), # 0: black
                              ('#cd0000', '#ff0000'), # 1: red
                              ('#00cd00', '#00ff00'), # 2: green
                              ('#cdcd00', '#ffff00'), # 3: yellow
                              ('#0000ee', '#0000ff'), # 4: blue
                              ('#cd00cd', '#ff00ff'), # 5: magenta
                              ('#00cdcd', '#00ffff'), # 6: cyan
                              ('#e5e5e5', '#ffffff')) # 7: white
         self.reset()
         
     def set_code(self, code):
         """ Set attributes based on code.
         """
         if code == 0:
             self.reset()
         elif code == 1:
             self.intensity = 1
             self.bold = True
         elif code == 3:
             self.italic = True
         elif code == 4:
             self.underline = True
         elif code == 22:
             self.intensity = 0
             self.bold = False
         elif code == 23:
             self.italic = False
         elif code == 24:
             self.underline = False
         elif code >= 30 and code <= 37:
             self.foreground_color = code - 30
         elif code == 39:
             self.foreground_color = None
         elif code >= 40 and code <= 47:
             self.background_color = code - 40
         elif code == 49:
             self.background_color = None
         
     def reset(self):
         """ Reset attributs to their default values.
         """
         self.intensity = 0
         self.italic = False
         self.bold = False
         self.underline = False
         self.foreground_color = None
         self.background_color = None
 
 
 class QtAnsiCodeProcessor(AnsiCodeProcessor):
     """ Translates ANSI escape codes into QTextCharFormats.
     """
     
     def get_format(self):
         """ Returns a QTextCharFormat that encodes the current style attributes.
         """
         format = QtGui.QTextCharFormat()
 
         # Set foreground color
         if self.foreground_color is not None:
             color = self.ansi_colors[self.foreground_color][self.intensity]
             format.setForeground(QtGui.QColor(color))
 
         # Set background color
         if self.background_color is not None:
             color = self.ansi_colors[self.background_color][self.intensity]
             format.setBackground(QtGui.QColor(color))
 
         # Set font weight/style options
         if self.bold:
             format.setFontWeight(QtGui.QFont.Bold)
         else:
             format.setFontWeight(QtGui.QFont.Normal)
         format.setFontItalic(self.italic)
         format.setFontUnderline(self.underline)
 
         return format
 
 
 class ConsoleWidget(QtGui.QPlainTextEdit):
     """ Base class for console-type widgets. This class is mainly concerned with
         dealing with the prompt, keeping the cursor inside the editing line, and
         handling ANSI escape sequences.
     """
 
     # Whether to process ANSI escape codes.
     ansi_codes = True
 
     # The maximum number of lines of text before truncation.
     buffer_size = 500
 
     # Whether to use a CompletionWidget or plain text output for tab completion.
     gui_completion = True
 
     # 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 = False
 
     # Protected class variables.
     _ansi_pattern = re.compile('\x01?\x1b\[(.*?)m\x02?')
     _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_E : QtCore.Qt.Key_End,
                          QtCore.Qt.Key_P : QtCore.Qt.Key_Up,
                          QtCore.Qt.Key_N : QtCore.Qt.Key_Down,
                          QtCore.Qt.Key_D : QtCore.Qt.Key_Delete, }
     _shortcuts = set(_ctrl_down_remap.keys() +
                      [ QtCore.Qt.Key_C, QtCore.Qt.Key_V ])
 
     #---------------------------------------------------------------------------
     # 'QObject' interface
     #---------------------------------------------------------------------------
 
     def __init__(self, parent=None):
         QtGui.QPlainTextEdit.__init__(self, parent)
 
         # Initialize protected variables.
         self._ansi_processor = QtAnsiCodeProcessor()
         self._completion_widget = CompletionWidget(self)
         self._continuation_prompt = '> '
         self._executing = False
         self._prompt = ''
         self._prompt_pos = 0
         self._reading = False
         self._reading_callback = None
 
         # Set a monospaced font.
         self.reset_font()
 
         # Define a custom context menu.
         self._context_menu = QtGui.QMenu(self)
 
         copy_action = QtGui.QAction('Copy', self)
         copy_action.triggered.connect(self.copy)
         self.copyAvailable.connect(copy_action.setEnabled)
         self._context_menu.addAction(copy_action)
 
         self._paste_action = QtGui.QAction('Paste', self)
         self._paste_action.triggered.connect(self.paste)
         self._context_menu.addAction(self._paste_action)
         self._context_menu.addSeparator()
 
         select_all_action = QtGui.QAction('Select All', self)
         select_all_action.triggered.connect(self.selectAll)
         self._context_menu.addAction(select_all_action)
 
     def event(self, event):
         """ Reimplemented to override shortcuts, if necessary.
         """
         # On Mac OS, it is always unnecessary to override shortcuts, hence the
         # check below. Users should just use the Control key instead of the
         # Command key.
         if self.override_shortcuts and \
                 sys.platform != 'darwin' and \
                 event.type() == QtCore.QEvent.ShortcutOverride and \
                 self._control_down(event.modifiers()) and \
                 event.key() in self._shortcuts:
             event.accept()
             return True
         else:
             return QtGui.QPlainTextEdit.event(self, event)
 
     #---------------------------------------------------------------------------
     # 'QWidget' interface
     #---------------------------------------------------------------------------
 
     def contextMenuEvent(self, event):
         """ Reimplemented to create a menu without destructive actions like
             'Cut' and 'Delete'.
         """
         clipboard_empty = QtGui.QApplication.clipboard().text().isEmpty()
         self._paste_action.setEnabled(not clipboard_empty)
         
         self._context_menu.exec_(event.globalPos())
 
     def dragMoveEvent(self, event):
         """ Reimplemented to disable dropping text.
         """
         event.ignore()
 
     def keyPressEvent(self, event):
         """ Reimplemented to create a console-like interface.
         """
         intercepted = False
         cursor = self.textCursor()
         position = cursor.position()
         key = event.key()
         ctrl_down = self._control_down(event.modifiers())
         alt_down = event.modifiers() & QtCore.Qt.AltModifier
         shift_down = event.modifiers() & QtCore.Qt.ShiftModifier
 
         # Even though we have reimplemented 'paste', the C++ level slot is still
         # called by Qt. So we intercept the key press here.
         if event.matches(QtGui.QKeySequence.Paste):
             self.paste()
             intercepted = True
 
         elif ctrl_down:
             if key in self._ctrl_down_remap:
                 ctrl_down = False
                 key = self._ctrl_down_remap[key]
                 event = QtGui.QKeyEvent(QtCore.QEvent.KeyPress, key, 
                                         QtCore.Qt.NoModifier)
 
             elif key == QtCore.Qt.Key_K:
                 if self._in_buffer(position):
                     cursor.movePosition(QtGui.QTextCursor.EndOfLine,
                                         QtGui.QTextCursor.KeepAnchor)
                     cursor.removeSelectedText()
                 intercepted = True
 
             elif key == QtCore.Qt.Key_X:
                 intercepted = True
 
             elif key == QtCore.Qt.Key_Y:
                 self.paste()
                 intercepted = True
 
         elif alt_down:
             if key == QtCore.Qt.Key_B:
                 self.setTextCursor(self._get_word_start_cursor(position))
                 intercepted = True
                 
             elif key == QtCore.Qt.Key_F:
                 self.setTextCursor(self._get_word_end_cursor(position))
                 intercepted = True
 
             elif key == QtCore.Qt.Key_Backspace:
                 cursor = self._get_word_start_cursor(position)
                 cursor.setPosition(position, QtGui.QTextCursor.KeepAnchor)
                 cursor.removeSelectedText()
                 intercepted = True
 
             elif key == QtCore.Qt.Key_D:
                 cursor = self._get_word_end_cursor(position)
                 cursor.setPosition(position, QtGui.QTextCursor.KeepAnchor)
                 cursor.removeSelectedText()
                 intercepted = True
 
         if self._completion_widget.isVisible():
             self._completion_widget.keyPressEvent(event)
             intercepted = event.isAccepted()
         
         else:
             if key in (QtCore.Qt.Key_Return, QtCore.Qt.Key_Enter):
                 if self._reading:
                     self.appendPlainText('\n')
                     self._reading = False
                     if self._reading_callback:
                         self._reading_callback()
-                        self._reading_callback = None
                 elif not self._executing:
                     self.execute(interactive=True)
                 intercepted = True
 
             elif key == QtCore.Qt.Key_Up:
                 if self._reading or not self._up_pressed():
                     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():
                     intercepted = True
                 else:
                     end_line = self._get_end_cursor().blockNumber()
                     intercepted = cursor.blockNumber() == end_line
 
             elif key == QtCore.Qt.Key_Tab:
                 if self._reading:
                     intercepted = False
                 else:
                     intercepted = not self._tab_pressed()
 
             elif key == QtCore.Qt.Key_Left:
                 intercepted = not self._in_buffer(position - 1)
 
             elif key == QtCore.Qt.Key_Home:
                 cursor.movePosition(QtGui.QTextCursor.StartOfLine)
                 start_pos = cursor.position()
                 start_line = cursor.blockNumber()
                 if start_line == self._get_prompt_cursor().blockNumber():
                     start_pos += len(self._prompt)
                 else:
                     start_pos += len(self._continuation_prompt)
                 if shift_down and self._in_buffer(position):
                     self._set_selection(position, start_pos)
                 else:
                     self._set_position(start_pos)
                 intercepted = True
 
             elif key == QtCore.Qt.Key_Backspace and not alt_down:
 
                 # Line deletion (remove continuation prompt)
                 len_prompt = len(self._continuation_prompt)
                 if not self._reading and \
                         cursor.columnNumber() == len_prompt and \
                         position != self._prompt_pos:
                     cursor.setPosition(position - len_prompt, 
                                        QtGui.QTextCursor.KeepAnchor)
                     cursor.removeSelectedText()
 
                 # 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:
                 anchor = cursor.anchor()
                 intercepted = not self._in_buffer(min(anchor, position))
 
         # Don't move cursor if control is down to allow copy-paste using
         # the keyboard in any part of the buffer.
         if not ctrl_down:
             self._keep_cursor_in_buffer()
 
         if not intercepted:
             QtGui.QPlainTextEdit.keyPressEvent(self, event)
 
     #--------------------------------------------------------------------------
     # 'QPlainTextEdit' interface
     #--------------------------------------------------------------------------
 
     def appendPlainText(self, text):
         """ Reimplemented to not append text as a new paragraph, which doesn't
             make sense for a console widget. Also, if enabled, handle ANSI
             codes.
         """
         cursor = self.textCursor()
         cursor.movePosition(QtGui.QTextCursor.End)
 
         if self.ansi_codes:
             format = QtGui.QTextCharFormat()
             previous_end = 0
             for match in self._ansi_pattern.finditer(text):
                 cursor.insertText(text[previous_end:match.start()], format)
                 previous_end = match.end()
                 for code in match.group(1).split(';'):
                     self._ansi_processor.set_code(int(code))
                 format = self._ansi_processor.get_format()
             cursor.insertText(text[previous_end:], format)
         else:
             cursor.insertText(text)
 
     def clear(self, keep_input=False):
-        """ Reimplemented to write a new prompt. If 'keep_input' is set,
-            restores the old input buffer when the new prompt is written.
+        """ Reimplemented to cancel reading and write a new prompt. If
+            'keep_input' is set, restores the old input buffer when the new
+            prompt is written.
         """
         super(ConsoleWidget, self).clear()
 
-        if keep_input:
+        input_buffer = ''
+        if self._reading:
+            self._reading = False
+        elif keep_input:
             input_buffer = self.input_buffer
         self._show_prompt()
-        if keep_input:
             self.input_buffer = input_buffer
 
     def paste(self):
         """ Reimplemented to ensure that text is pasted in the editing region.
         """
         self._keep_cursor_in_buffer()
         QtGui.QPlainTextEdit.paste(self)
 
     def print_(self, printer):
         """ Reimplemented to work around a bug in PyQt: the C++ level 'print_'
             slot has the wrong signature.
         """
         QtGui.QPlainTextEdit.print_(self, printer)
 
     #---------------------------------------------------------------------------
     # 'ConsoleWidget' public interface
     #---------------------------------------------------------------------------
 
     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 not possible to prompt for more input.
 
         Returns:
         --------
         A boolean indicating whether the source was executed.
         """
         if not hidden:
             if source is not None:
                 self.input_buffer = source
 
             self.appendPlainText('\n')
             self._executing_input_buffer = self.input_buffer
             self._executing = True
             self._prompt_finished()
 
         real_source = self.input_buffer if source is None else source
         complete = self._is_complete(real_source, interactive)
         if complete:
             if not hidden:
                 # The maximum block count is only in effect during execution.
                 # This ensures that _prompt_pos does not become invalid due to
                 # text truncation.
                 self.setMaximumBlockCount(self.buffer_size)
             self._execute(real_source, hidden)
         elif hidden:
             raise RuntimeError('Incomplete noninteractive input: "%s"' % source)
         else:
             self._show_continuation_prompt()
 
         return complete
 
     def _get_input_buffer(self):
         """ The text that the user has entered entered at the current prompt.
         """
         # 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:
             return self._executing_input_buffer
 
         cursor = self._get_end_cursor()
         cursor.setPosition(self._prompt_pos, QtGui.QTextCursor.KeepAnchor)
 
         # Use QTextDocumentFragment intermediate object because it strips
         # out the Unicode line break characters that Qt insists on inserting.
         input_buffer = str(cursor.selection().toPlainText())
 
         # Strip out continuation prompts.
         return input_buffer.replace('\n' + self._continuation_prompt, '\n')
 
     def _set_input_buffer(self, string):
         """ Replaces the text in the input buffer with 'string'.
         """
         # Add continuation prompts where necessary.
         lines = string.splitlines()
         for i in xrange(1, len(lines)):
             lines[i] = self._continuation_prompt + lines[i]
         string = '\n'.join(lines)
 
         # Replace buffer with new text.
         cursor = self._get_end_cursor()
         cursor.setPosition(self._prompt_pos, QtGui.QTextCursor.KeepAnchor)
         cursor.insertText(string)
         self.moveCursor(QtGui.QTextCursor.End)
 
     input_buffer = property(_get_input_buffer, _set_input_buffer)
 
     def _get_input_buffer_cursor_line(self):
         """ The text in the line of the input buffer in which the user's cursor
             rests. Returns a string if there is such a line; otherwise, None.
         """
         if self._executing:
             return None
         cursor = self.textCursor()
         if cursor.position() >= self._prompt_pos:
             text = str(cursor.block().text())
             if cursor.blockNumber() == self._get_prompt_cursor().blockNumber():
                 return text[len(self._prompt):]
             else:
                 return text[len(self._continuation_prompt):]
         else:
             return None
 
     input_buffer_cursor_line = property(_get_input_buffer_cursor_line)
 
     def _get_font(self):
         """ The base font being used by the ConsoleWidget.
         """
         return self.document().defaultFont()
 
     def _set_font(self, font):
         """ Sets the base font for the ConsoleWidget to the specified QFont.
         """
         self._completion_widget.setFont(font)
         self.document().setDefaultFont(font)
 
     font = property(_get_font, _set_font)
 
     def reset_font(self):
         """ Sets the font to the default fixed-width font for this platform.
         """
         if sys.platform == 'win32':
             name = 'Courier'
         elif sys.platform == 'darwin':
             name = 'Monaco'
         else:
             name = 'Monospace'
         font = QtGui.QFont(name, QtGui.qApp.font().pointSize())
         font.setStyleHint(QtGui.QFont.TypeWriter)
         self._set_font(font)
         
     #---------------------------------------------------------------------------
     # '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):
         """ Called when the up key is pressed. Returns whether to continue
             processing the event.
         """
         return True
 
     def _down_pressed(self):
         """ 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 _control_down(self, modifiers):
         """ Given a KeyboardModifiers flags object, return whether the Control
             key is down (on Mac OS, treat the Command key as a synonym for
             Control).
         """
         down = bool(modifiers & QtCore.Qt.ControlModifier)
 
         # Note: on Mac OS, ControlModifier corresponds to the Command key while
         # MetaModifier corresponds to the Control key.
         if sys.platform == 'darwin':
             down = down ^ bool(modifiers & QtCore.Qt.MetaModifier)
             
         return down
     
     def _complete_with_items(self, cursor, items):
         """ Performs completion with 'items' at the specified cursor location.
         """
         if len(items) == 1:
             cursor.setPosition(self.textCursor().position(), 
                                QtGui.QTextCursor.KeepAnchor)
             cursor.insertText(items[0])
         elif len(items) > 1:
             if self.gui_completion:
                 self._completion_widget.show_items(cursor, items) 
             else:
                 text = '\n'.join(items) + '\n'
                 self._write_text_keeping_prompt(text)
                 
     def _get_end_cursor(self):
         """ Convenience method that returns a cursor for the last character.
         """
         cursor = self.textCursor()
         cursor.movePosition(QtGui.QTextCursor.End)
         return cursor
 
     def _get_prompt_cursor(self):
         """ Convenience method that returns a cursor for the prompt position.
         """
         cursor = self.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.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.document()
         position -= 1
         while self._in_buffer(position) and \
                 not document.characterAt(position).isLetterOrNumber():
             position -= 1
         while self._in_buffer(position) and \
                 document.characterAt(position).isLetterOrNumber():
             position -= 1
         cursor = self.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.document()
         end = self._get_end_cursor().position()
         while position < end and \
                 not document.characterAt(position).isLetterOrNumber():
             position += 1
         while position < end and \
                 document.characterAt(position).isLetterOrNumber():
             position += 1
         cursor = self.textCursor()
         cursor.setPosition(position)
         return cursor
 
     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.setMaximumBlockCount(0)
         self.setUndoRedoEnabled(True)
 
         self.setReadOnly(False)
         self.moveCursor(QtGui.QTextCursor.End)
         self.centerCursor()
 
         self._executing = False
         self._prompt_started_hook()
 
     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.setUndoRedoEnabled(False)
         self.setReadOnly(True)
         self._prompt_finished_hook()
 
     def _readline(self, prompt='', callback=None):
         """ 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
         self._show_prompt(prompt, newline=False)
 
         if callback is None:
             self._reading_callback = None
             while self._reading:
                 QtCore.QCoreApplication.processEvents()
             return self.input_buffer.rstrip('\n')
 
         else:
             self._reading_callback = lambda: \
                 callback(self.input_buffer.rstrip('\n'))
 
     def _set_position(self, position):
         """ Convenience method to set the position of the cursor.
         """
         cursor = self.textCursor()
         cursor.setPosition(position)
         self.setTextCursor(cursor)
 
     def _set_selection(self, start, end):
         """ Convenience method to set the current selected text.
         """
         self.setTextCursor(self._get_selection_cursor(start, end))
 
     def _show_prompt(self, prompt=None, 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.
 
         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.
         """
         if newline:
             cursor = self._get_end_cursor()
             if cursor.position() > 0:
                 cursor.movePosition(QtGui.QTextCursor.Left, 
                                     QtGui.QTextCursor.KeepAnchor)
                 if str(cursor.selection().toPlainText()) != '\n':
                     self.appendPlainText('\n')
 
         if prompt is not None:
             self._prompt = prompt
         self.appendPlainText(self._prompt)
 
         self._prompt_pos = self._get_end_cursor().position()
         self._prompt_started()
 
     def _show_continuation_prompt(self):
         """ Writes a new continuation prompt at the end of the buffer.
         """
         self.appendPlainText(self._continuation_prompt)
         self._prompt_started()
 
     def _write_text_keeping_prompt(self, text):
         """ Writes 'text' after the current prompt, then restores the old prompt
             with its old input buffer.
         """
         input_buffer = self.input_buffer
         self.appendPlainText('\n')
         self._prompt_finished()
 
         self.appendPlainText(text)
         self._show_prompt()
         self.input_buffer = input_buffer
 
     def _in_buffer(self, position):
         """ Returns whether the given position is inside the editing region.
         """
         return position >= self._prompt_pos
 
     def _keep_cursor_in_buffer(self):
         """ Ensures that the cursor is inside the editing region. Returns
             whether the cursor was moved.
         """
         cursor = self.textCursor()
         if cursor.position() < self._prompt_pos:
             cursor.movePosition(QtGui.QTextCursor.End)
             self.setTextCursor(cursor)
             return True
         else:
             return False
 
 
 class HistoryConsoleWidget(ConsoleWidget):
     """ A ConsoleWidget that keeps a history of the commands that have been
         executed.
     """
     
     #---------------------------------------------------------------------------
     # 'QObject' interface
     #---------------------------------------------------------------------------
 
     def __init__(self, parent=None):
         super(HistoryConsoleWidget, self).__init__(parent)
 
         self._history = []
         self._history_index = 0
 
     #---------------------------------------------------------------------------
     # 'ConsoleWidget' public interface
     #---------------------------------------------------------------------------
 
     def execute(self, source=None, hidden=False, interactive=False):
         """ Reimplemented to the store history.
         """
         if not hidden:
             history = self.input_buffer if source is None else source
 
         executed = super(HistoryConsoleWidget, self).execute(
             source, hidden, interactive)
 
         if executed and not hidden:
             self._history.append(history.rstrip())
             self._history_index = len(self._history)
 
         return executed
 
     #---------------------------------------------------------------------------
     # 'ConsoleWidget' abstract interface
     #---------------------------------------------------------------------------
 
     def _up_pressed(self):
         """ Called when the up key is pressed. Returns whether to continue
             processing the event.
         """
         prompt_cursor = self._get_prompt_cursor()
         if self.textCursor().blockNumber() == prompt_cursor.blockNumber():
             self.history_previous()
 
             # Go to the first line of prompt for seemless history scrolling.
             cursor = self._get_prompt_cursor()
             cursor.movePosition(QtGui.QTextCursor.EndOfLine)
             self.setTextCursor(cursor)
 
             return False
         return True
 
     def _down_pressed(self):
         """ Called when the down key is pressed. Returns whether to continue
             processing the event.
         """
         end_cursor = self._get_end_cursor()
         if self.textCursor().blockNumber() == end_cursor.blockNumber():
             self.history_next()
             return False
         return True
 
     #---------------------------------------------------------------------------
     # 'HistoryConsoleWidget' interface
     #---------------------------------------------------------------------------
 
     def history_previous(self):
         """ If possible, set the input buffer to the previous item in the
             history.
         """
         if self._history_index > 0:
             self._history_index -= 1
             self.input_buffer = self._history[self._history_index]
 
     def history_next(self):
         """ Set the input buffer to the next item in the history, or a blank
             line if there is no subsequent item.
         """
         if self._history_index < len(self._history):
             self._history_index += 1
             if self._history_index < len(self._history):
                 self.input_buffer = self._history[self._history_index]
             else:
                 self.input_buffer = ''