Merge pull request #4091 from takluyver/qt-banner-config

Make Qt console banner configurable

IPython/qt/console/frontend_widget.py

@@ -1,784 +1,784
 from __future__ import print_function
 
 # Standard library imports
 from collections import namedtuple
 import sys
 import uuid
 
 # System library imports
 from pygments.lexers import PythonLexer
 from IPython.external import qt
 from IPython.external.qt import QtCore, QtGui
 
 # Local imports
 from IPython.core.inputsplitter import InputSplitter, IPythonInputSplitter
 from IPython.core.inputtransformer import classic_prompt
 from IPython.core.oinspect import call_tip
 from IPython.qt.base_frontend_mixin import BaseFrontendMixin
 from IPython.utils.traitlets import Bool, Instance, Unicode
 from bracket_matcher import BracketMatcher
 from call_tip_widget import CallTipWidget
 from completion_lexer import CompletionLexer
 from history_console_widget import HistoryConsoleWidget
 from pygments_highlighter import PygmentsHighlighter
 
 
 class FrontendHighlighter(PygmentsHighlighter):
     """ A PygmentsHighlighter that understands and ignores prompts.
     """
 
     def __init__(self, frontend):
         super(FrontendHighlighter, self).__init__(frontend._control.document())
         self._current_offset = 0
         self._frontend = frontend
         self.highlighting_on = False
 
     def highlightBlock(self, string):
         """ Highlight a block of text. Reimplemented to highlight selectively.
         """
         if not self.highlighting_on:
             return
 
         # The input to this function is a unicode string that may contain
         # paragraph break characters, non-breaking spaces, etc. Here we acquire
         # the string as plain text so we can compare it.
         current_block = self.currentBlock()
         string = self._frontend._get_block_plain_text(current_block)
 
         # Decide whether to check for the regular or continuation prompt.
         if current_block.contains(self._frontend._prompt_pos):
             prompt = self._frontend._prompt
         else:
             prompt = self._frontend._continuation_prompt
 
         # Only highlight if we can identify a prompt, but make sure not to
         # highlight the prompt.
         if string.startswith(prompt):
             self._current_offset = len(prompt)
             string = string[len(prompt):]
             super(FrontendHighlighter, self).highlightBlock(string)
 
     def rehighlightBlock(self, block):
         """ Reimplemented to temporarily enable highlighting if disabled.
         """
         old = self.highlighting_on
         self.highlighting_on = True
         super(FrontendHighlighter, self).rehighlightBlock(block)
         self.highlighting_on = old
 
     def setFormat(self, start, count, format):
         """ Reimplemented to highlight selectively.
         """
         start += self._current_offset
         super(FrontendHighlighter, self).setFormat(start, count, format)
 
 
 class FrontendWidget(HistoryConsoleWidget, BaseFrontendMixin):
     """ A Qt frontend for a generic Python kernel.
     """
 
     # The text to show when the kernel is (re)started.
-    banner = Unicode()
+    banner = Unicode(config=True)
 
     # An option and corresponding signal for overriding the default kernel
     # interrupt behavior.
     custom_interrupt = Bool(False)
     custom_interrupt_requested = QtCore.Signal()
 
     # An option and corresponding signals for overriding the default kernel
     # restart behavior.
     custom_restart = Bool(False)
     custom_restart_kernel_died = QtCore.Signal(float)
     custom_restart_requested = QtCore.Signal()
 
     # Whether to automatically show calltips on open-parentheses.
     enable_calltips = Bool(True, config=True,
         help="Whether to draw information calltips on open-parentheses.")
 
     clear_on_kernel_restart = Bool(True, config=True,
         help="Whether to clear the console when the kernel is restarted")
 
     confirm_restart = Bool(True, config=True,
         help="Whether to ask for user confirmation when restarting kernel")
 
     # Emitted when a user visible 'execute_request' has been submitted to the
     # kernel from the FrontendWidget. Contains the code to be executed.
     executing = QtCore.Signal(object)
 
     # Emitted when a user-visible 'execute_reply' has been received from the
     # kernel and processed by the FrontendWidget. Contains the response message.
     executed = QtCore.Signal(object)
 
     # Emitted when an exit request has been received from the kernel.
     exit_requested = QtCore.Signal(object)
 
     # Protected class variables.
     _prompt_transformer = IPythonInputSplitter(physical_line_transforms=[classic_prompt()],
                                                logical_line_transforms=[],
                                                python_line_transforms=[],
                                               )
     _CallTipRequest = namedtuple('_CallTipRequest', ['id', 'pos'])
     _CompletionRequest = namedtuple('_CompletionRequest', ['id', 'pos'])
     _ExecutionRequest = namedtuple('_ExecutionRequest', ['id', 'kind'])
     _input_splitter_class = InputSplitter
     _local_kernel = False
     _highlighter = Instance(FrontendHighlighter)
 
     #---------------------------------------------------------------------------
     # 'object' interface
     #---------------------------------------------------------------------------
 
     def __init__(self, *args, **kw):
         super(FrontendWidget, self).__init__(*args, **kw)
         # FIXME: remove this when PySide min version is updated past 1.0.7
         # forcefully disable calltips if PySide is < 1.0.7, because they crash
         if qt.QT_API == qt.QT_API_PYSIDE:
             import PySide
             if PySide.__version_info__ < (1,0,7):
                 self.log.warn("PySide %s < 1.0.7 detected, disabling calltips" % PySide.__version__)
                 self.enable_calltips = False
 
         # FrontendWidget protected variables.
         self._bracket_matcher = BracketMatcher(self._control)
         self._call_tip_widget = CallTipWidget(self._control)
         self._completion_lexer = CompletionLexer(PythonLexer())
         self._copy_raw_action = QtGui.QAction('Copy (Raw Text)', None)
         self._hidden = False
         self._highlighter = FrontendHighlighter(self)
         self._input_splitter = self._input_splitter_class()
         self._kernel_manager = None
         self._kernel_client = None
         self._request_info = {}
         self._request_info['execute'] = {};
         self._callback_dict = {}
 
         # Configure the ConsoleWidget.
         self.tab_width = 4
         self._set_continuation_prompt('... ')
 
         # Configure the CallTipWidget.
         self._call_tip_widget.setFont(self.font)
         self.font_changed.connect(self._call_tip_widget.setFont)
 
         # Configure actions.
         action = self._copy_raw_action
         key = QtCore.Qt.CTRL | QtCore.Qt.SHIFT | QtCore.Qt.Key_C
         action.setEnabled(False)
         action.setShortcut(QtGui.QKeySequence(key))
         action.setShortcutContext(QtCore.Qt.WidgetWithChildrenShortcut)
         action.triggered.connect(self.copy_raw)
         self.copy_available.connect(action.setEnabled)
         self.addAction(action)
 
         # Connect signal handlers.
         document = self._control.document()
         document.contentsChange.connect(self._document_contents_change)
 
         # Set flag for whether we are connected via localhost.
         self._local_kernel = kw.get('local_kernel',
                                     FrontendWidget._local_kernel)
 
     #---------------------------------------------------------------------------
     # 'ConsoleWidget' public interface
     #---------------------------------------------------------------------------
 
     def copy(self):
         """ Copy the currently selected text to the clipboard, removing prompts.
         """
         if self._page_control is not None and self._page_control.hasFocus():
             self._page_control.copy()
         elif self._control.hasFocus():
             text = self._control.textCursor().selection().toPlainText()
             if text:
                 text = self._prompt_transformer.transform_cell(text)
                 QtGui.QApplication.clipboard().setText(text)
         else:
             self.log.debug("frontend widget : unknown copy target")
 
     #---------------------------------------------------------------------------
     # 'ConsoleWidget' abstract interface
     #---------------------------------------------------------------------------
 
     def _is_complete(self, source, interactive):
         """ Returns whether 'source' can be completely processed and a new
             prompt created. When triggered by an Enter/Return key press,
             'interactive' is True; otherwise, it is False.
         """
         self._input_splitter.reset()
         complete = self._input_splitter.push(source)
         if interactive:
             complete = not self._input_splitter.push_accepts_more()
         return complete
 
     def _execute(self, source, hidden):
         """ Execute 'source'. If 'hidden', do not show any output.
 
         See parent class :meth:`execute` docstring for full details.
         """
         msg_id = self.kernel_client.execute(source, hidden)
         self._request_info['execute'][msg_id] = self._ExecutionRequest(msg_id, 'user')
         self._hidden = hidden
         if not hidden:
             self.executing.emit(source)
 
     def _prompt_started_hook(self):
         """ Called immediately after a new prompt is displayed.
         """
         if not self._reading:
             self._highlighter.highlighting_on = True
 
     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.
         """
         # Flush all state from the input splitter so the next round of
         # reading input starts with a clean buffer.
         self._input_splitter.reset()
 
         if not self._reading:
             self._highlighter.highlighting_on = False
 
     def _tab_pressed(self):
         """ Called when the tab key is pressed. Returns whether to continue
             processing the event.
         """
         # Perform tab completion if:
         # 1) The cursor is in the input buffer.
         # 2) There is a non-whitespace character before the cursor.
         text = self._get_input_buffer_cursor_line()
         if text is None:
             return False
         complete = bool(text[:self._get_input_buffer_cursor_column()].strip())
         if complete:
             self._complete()
         return not complete
 
     #---------------------------------------------------------------------------
     # 'ConsoleWidget' protected interface
     #---------------------------------------------------------------------------
 
     def _context_menu_make(self, pos):
         """ Reimplemented to add an action for raw copy.
         """
         menu = super(FrontendWidget, self)._context_menu_make(pos)
         for before_action in menu.actions():
             if before_action.shortcut().matches(QtGui.QKeySequence.Paste) == \
                     QtGui.QKeySequence.ExactMatch:
                 menu.insertAction(before_action, self._copy_raw_action)
                 break
         return menu
 
     def request_interrupt_kernel(self):
         if self._executing:
             self.interrupt_kernel()
 
     def request_restart_kernel(self):
         message = 'Are you sure you want to restart the kernel?'
         self.restart_kernel(message, now=False)
 
     def _event_filter_console_keypress(self, event):
         """ Reimplemented for execution interruption and smart backspace.
         """
         key = event.key()
         if self._control_key_down(event.modifiers(), include_command=False):
 
             if key == QtCore.Qt.Key_C and self._executing:
                 self.request_interrupt_kernel()
                 return True
 
             elif key == QtCore.Qt.Key_Period:
                 self.request_restart_kernel()
                 return True
 
         elif not event.modifiers() & QtCore.Qt.AltModifier:
 
             # Smart backspace: remove four characters in one backspace if:
             # 1) everything left of the cursor is whitespace
             # 2) the four characters immediately left of the cursor are spaces
             if key == QtCore.Qt.Key_Backspace:
                 col = self._get_input_buffer_cursor_column()
                 cursor = self._control.textCursor()
                 if col > 3 and not cursor.hasSelection():
                     text = self._get_input_buffer_cursor_line()[:col]
                     if text.endswith('    ') and not text.strip():
                         cursor.movePosition(QtGui.QTextCursor.Left,
                                             QtGui.QTextCursor.KeepAnchor, 4)
                         cursor.removeSelectedText()
                         return True
 
         return super(FrontendWidget, self)._event_filter_console_keypress(event)
 
     def _insert_continuation_prompt(self, cursor):
         """ Reimplemented for auto-indentation.
         """
         super(FrontendWidget, self)._insert_continuation_prompt(cursor)
         cursor.insertText(' ' * self._input_splitter.indent_spaces)
 
     #---------------------------------------------------------------------------
     # 'BaseFrontendMixin' abstract interface
     #---------------------------------------------------------------------------
 
     def _handle_complete_reply(self, rep):
         """ Handle replies for tab completion.
         """
         self.log.debug("complete: %s", rep.get('content', ''))
         cursor = self._get_cursor()
         info = self._request_info.get('complete')
         if info and info.id == rep['parent_header']['msg_id'] and \
                 info.pos == cursor.position():
             text = '.'.join(self._get_context())
             cursor.movePosition(QtGui.QTextCursor.Left, n=len(text))
             self._complete_with_items(cursor, rep['content']['matches'])
 
     def _silent_exec_callback(self, expr, callback):
         """Silently execute `expr` in the kernel and call `callback` with reply
 
         the `expr` is evaluated silently in the kernel (without) output in
         the frontend. Call `callback` with the
         `repr <http://docs.python.org/library/functions.html#repr> `_ as first argument
 
         Parameters
         ----------
         expr : string
             valid string to be executed by the kernel.
         callback : function
             function accepting one argument, as a string. The string will be
             the `repr` of the result of evaluating `expr`
 
         The `callback` is called with the `repr()` of the result of `expr` as
         first argument. To get the object, do `eval()` on the passed value.
 
         See Also
         --------
         _handle_exec_callback : private method, deal with calling callback with reply
 
         """
 
         # generate uuid, which would be used as an indication of whether or
         # not the unique request originated from here (can use msg id ?)
         local_uuid = str(uuid.uuid1())
         msg_id = self.kernel_client.execute('',
             silent=True, user_expressions={ local_uuid:expr })
         self._callback_dict[local_uuid] = callback
         self._request_info['execute'][msg_id] = self._ExecutionRequest(msg_id, 'silent_exec_callback')
 
     def _handle_exec_callback(self, msg):
         """Execute `callback` corresponding to `msg` reply, after ``_silent_exec_callback``
 
         Parameters
         ----------
         msg : raw message send by the kernel containing an `user_expressions`
                 and having a 'silent_exec_callback' kind.
 
         Notes
         -----
         This function will look for a `callback` associated with the
         corresponding message id. Association has been made by
         `_silent_exec_callback`. `callback` is then called with the `repr()`
         of the value of corresponding `user_expressions` as argument.
         `callback` is then removed from the known list so that any message
         coming again with the same id won't trigger it.
 
         """
 
         user_exp = msg['content'].get('user_expressions')
         if not user_exp:
             return
         for expression in user_exp:
             if expression in self._callback_dict:
                 self._callback_dict.pop(expression)(user_exp[expression])
 
     def _handle_execute_reply(self, msg):
         """ Handles replies for code execution.
         """
         self.log.debug("execute: %s", msg.get('content', ''))
         msg_id = msg['parent_header']['msg_id']
         info = self._request_info['execute'].get(msg_id)
         # unset reading flag, because if execute finished, raw_input can't
         # still be pending.
         self._reading = False
         if info and info.kind == 'user' and not self._hidden:
             # Make sure that all output from the SUB channel has been processed
             # before writing a new prompt.
             self.kernel_client.iopub_channel.flush()
 
             # Reset the ANSI style information to prevent bad text in stdout
             # from messing up our colors. We're not a true terminal so we're
             # allowed to do this.
             if self.ansi_codes:
                 self._ansi_processor.reset_sgr()
 
             content = msg['content']
             status = content['status']
             if status == 'ok':
                 self._process_execute_ok(msg)
             elif status == 'error':
                 self._process_execute_error(msg)
             elif status == 'aborted':
                 self._process_execute_abort(msg)
 
             self._show_interpreter_prompt_for_reply(msg)
             self.executed.emit(msg)
             self._request_info['execute'].pop(msg_id)
         elif info and info.kind == 'silent_exec_callback' and not self._hidden:
             self._handle_exec_callback(msg)
             self._request_info['execute'].pop(msg_id)
         else:
             super(FrontendWidget, self)._handle_execute_reply(msg)
 
     def _handle_input_request(self, msg):
         """ Handle requests for raw_input.
         """
         self.log.debug("input: %s", msg.get('content', ''))
         if self._hidden:
             raise RuntimeError('Request for raw input during hidden execution.')
 
         # Make sure that all output from the SUB channel has been processed
         # before entering readline mode.
         self.kernel_client.iopub_channel.flush()
 
         def callback(line):
             self.kernel_client.stdin_channel.input(line)
         if self._reading:
             self.log.debug("Got second input request, assuming first was interrupted.")
             self._reading = False
         self._readline(msg['content']['prompt'], callback=callback)
 
     def _kernel_restarted_message(self, died=True):
         msg = "Kernel died, restarting" if died else "Kernel restarting"
         self._append_html("<br>%s<hr><br>" % msg,
             before_prompt=False
         )
 
     def _handle_kernel_died(self, since_last_heartbeat):
         """Handle the kernel's death (if we do not own the kernel).
         """
         self.log.warn("kernel died: %s", since_last_heartbeat)
         if self.custom_restart:
             self.custom_restart_kernel_died.emit(since_last_heartbeat)
         else:
             self._kernel_restarted_message(died=True)
             self.reset()
 
     def _handle_kernel_restarted(self, died=True):
         """Notice that the autorestarter restarted the kernel.
 
         There's nothing to do but show a message.
         """
         self.log.warn("kernel restarted")
         self._kernel_restarted_message(died=died)
         self.reset()
 
     def _handle_object_info_reply(self, rep):
         """ Handle replies for call tips.
         """
         self.log.debug("oinfo: %s", rep.get('content', ''))
         cursor = self._get_cursor()
         info = self._request_info.get('call_tip')
         if info and info.id == rep['parent_header']['msg_id'] and \
                 info.pos == cursor.position():
             # Get the information for a call tip.  For now we format the call
             # line as string, later we can pass False to format_call and
             # syntax-highlight it ourselves for nicer formatting in the
             # calltip.
             content = rep['content']
             # if this is from pykernel, 'docstring' will be the only key
             if content.get('ismagic', False):
                 # Don't generate a call-tip for magics. Ideally, we should
                 # generate a tooltip, but not on ( like we do for actual
                 # callables.
                 call_info, doc = None, None
             else:
                 call_info, doc = call_tip(content, format_call=True)
             if call_info or doc:
                 self._call_tip_widget.show_call_info(call_info, doc)
 
     def _handle_pyout(self, msg):
         """ Handle display hook output.
         """
         self.log.debug("pyout: %s", msg.get('content', ''))
         if not self._hidden and self._is_from_this_session(msg):
             text = msg['content']['data']
             self._append_plain_text(text + '\n', before_prompt=True)
 
     def _handle_stream(self, msg):
         """ Handle stdout, stderr, and stdin.
         """
         self.log.debug("stream: %s", msg.get('content', ''))
         if not self._hidden and self._is_from_this_session(msg):
             # Most consoles treat tabs as being 8 space characters. Convert tabs
             # to spaces so that output looks as expected regardless of this
             # widget's tab width.
             text = msg['content']['data'].expandtabs(8)
 
             self._append_plain_text(text, before_prompt=True)
             self._control.moveCursor(QtGui.QTextCursor.End)
 
     def _handle_shutdown_reply(self, msg):
         """ Handle shutdown signal, only if from other console.
         """
         self.log.warn("shutdown: %s", msg.get('content', ''))
         restart = msg.get('content', {}).get('restart', False)
         if not self._hidden and not self._is_from_this_session(msg):
             # got shutdown reply, request came from session other than ours
             if restart:
                 # someone restarted the kernel, handle it
                 self._handle_kernel_restarted(died=False)
             else:
                 # kernel was shutdown permanently
                 # this triggers exit_requested if the kernel was local,
                 # and a dialog if the kernel was remote,
                 # so we don't suddenly clear the qtconsole without asking.
                 if self._local_kernel:
                     self.exit_requested.emit(self)
                 else:
                     title = self.window().windowTitle()
                     reply = QtGui.QMessageBox.question(self, title,
                         "Kernel has been shutdown permanently. "
                         "Close the Console?",
                         QtGui.QMessageBox.Yes,QtGui.QMessageBox.No)
                     if reply == QtGui.QMessageBox.Yes:
                         self.exit_requested.emit(self)
 
     def _handle_status(self, msg):
         """Handle status message"""
         # This is where a busy/idle indicator would be triggered,
         # when we make one.
         state = msg['content'].get('execution_state', '')
         if state == 'starting':
             # kernel started while we were running
             if self._executing:
                 self._handle_kernel_restarted(died=True)
         elif state == 'idle':
             pass
         elif state == 'busy':
             pass
 
     def _started_channels(self):
         """ Called when the KernelManager channels have started listening or
             when the frontend is assigned an already listening KernelManager.
         """
         self.reset(clear=True)
 
     #---------------------------------------------------------------------------
     # 'FrontendWidget' public interface
     #---------------------------------------------------------------------------
 
     def copy_raw(self):
         """ Copy the currently selected text to the clipboard without attempting
             to remove prompts or otherwise alter the text.
         """
         self._control.copy()
 
     def execute_file(self, path, hidden=False):
         """ Attempts to execute file with 'path'. If 'hidden', no output is
             shown.
         """
         self.execute('execfile(%r)' % path, hidden=hidden)
 
     def interrupt_kernel(self):
         """ Attempts to interrupt the running kernel.
         
         Also unsets _reading flag, to avoid runtime errors
         if raw_input is called again.
         """
         if self.custom_interrupt:
             self._reading = False
             self.custom_interrupt_requested.emit()
         elif self.kernel_manager:
             self._reading = False
             self.kernel_manager.interrupt_kernel()
         else:
             self._append_plain_text('Cannot interrupt a kernel I did not start.\n')
 
     def reset(self, clear=False):
         """ Resets the widget to its initial state if ``clear`` parameter
         is True, otherwise
         prints a visual indication of the fact that the kernel restarted, but
         does not clear the traces from previous usage of the kernel before it
         was restarted.  With ``clear=True``, it is similar to ``%clear``, but
         also re-writes the banner and aborts execution if necessary.
         """
         if self._executing:
             self._executing = False
             self._request_info['execute'] = {}
         self._reading = False
         self._highlighter.highlighting_on = False
 
         if clear:
             self._control.clear()
             self._append_plain_text(self.banner)
         # update output marker for stdout/stderr, so that startup
         # messages appear after banner:
         self._append_before_prompt_pos = self._get_cursor().position()
         self._show_interpreter_prompt()
 
     def restart_kernel(self, message, now=False):
         """ Attempts to restart the running kernel.
         """
         # FIXME: now should be configurable via a checkbox in the dialog.  Right
         # now at least the heartbeat path sets it to True and the manual restart
         # to False.  But those should just be the pre-selected states of a
         # checkbox that the user could override if so desired.  But I don't know
         # enough Qt to go implementing the checkbox now.
 
         if self.custom_restart:
             self.custom_restart_requested.emit()
             return
 
         if self.kernel_manager:
             # Pause the heart beat channel to prevent further warnings.
             self.kernel_client.hb_channel.pause()
 
             # Prompt the user to restart the kernel. Un-pause the heartbeat if
             # they decline. (If they accept, the heartbeat will be un-paused
             # automatically when the kernel is restarted.)
             if self.confirm_restart:
                 buttons = QtGui.QMessageBox.Yes | QtGui.QMessageBox.No
                 result = QtGui.QMessageBox.question(self, 'Restart kernel?',
                                                     message, buttons)
                 do_restart = result == QtGui.QMessageBox.Yes
             else:
                 # confirm_restart is False, so we don't need to ask user
                 # anything, just do the restart
                 do_restart = True
             if do_restart:
                 try:
                     self.kernel_manager.restart_kernel(now=now)
                 except RuntimeError as e:
                     self._append_plain_text(
                         'Error restarting kernel: %s\n' % e,
                         before_prompt=True
                     )
                 else:
                     self._append_html("<br>Restarting kernel...\n<hr><br>",
                         before_prompt=True,
                     )
             else:
                 self.kernel_client.hb_channel.unpause()
 
         else:
             self._append_plain_text(
                 'Cannot restart a Kernel I did not start\n',
                 before_prompt=True
             )
 
     #---------------------------------------------------------------------------
     # 'FrontendWidget' protected interface
     #---------------------------------------------------------------------------
 
     def _call_tip(self):
         """ Shows a call tip, if appropriate, at the current cursor location.
         """
         # Decide if it makes sense to show a call tip
         if not self.enable_calltips:
             return False
         cursor = self._get_cursor()
         cursor.movePosition(QtGui.QTextCursor.Left)
         if cursor.document().characterAt(cursor.position()) != '(':
             return False
         context = self._get_context(cursor)
         if not context:
             return False
 
         # Send the metadata request to the kernel
         name = '.'.join(context)
         msg_id = self.kernel_client.object_info(name)
         pos = self._get_cursor().position()
         self._request_info['call_tip'] = self._CallTipRequest(msg_id, pos)
         return True
 
     def _complete(self):
         """ Performs completion at the current cursor location.
         """
         context = self._get_context()
         if context:
             # Send the completion request to the kernel
             msg_id = self.kernel_client.complete(
                 '.'.join(context),                       # text
                 self._get_input_buffer_cursor_line(),    # line
                 self._get_input_buffer_cursor_column(),  # cursor_pos
                 self.input_buffer)                       # block
             pos = self._get_cursor().position()
             info = self._CompletionRequest(msg_id, pos)
             self._request_info['complete'] = info
 
     def _get_context(self, cursor=None):
         """ Gets the context for the specified cursor (or the current cursor
             if none is specified).
         """
         if cursor is None:
             cursor = self._get_cursor()
         cursor.movePosition(QtGui.QTextCursor.StartOfBlock,
                             QtGui.QTextCursor.KeepAnchor)
         text = cursor.selection().toPlainText()
         return self._completion_lexer.get_context(text)
 
     def _process_execute_abort(self, msg):
         """ Process a reply for an aborted execution request.
         """
         self._append_plain_text("ERROR: execution aborted\n")
 
     def _process_execute_error(self, msg):
         """ Process a reply for an execution request that resulted in an error.
         """
         content = msg['content']
         # If a SystemExit is passed along, this means exit() was called - also
         # all the ipython %exit magic syntax of '-k' to be used to keep
         # the kernel running
         if content['ename']=='SystemExit':
             keepkernel = content['evalue']=='-k' or content['evalue']=='True'
             self._keep_kernel_on_exit = keepkernel
             self.exit_requested.emit(self)
         else:
             traceback = ''.join(content['traceback'])
             self._append_plain_text(traceback)
 
     def _process_execute_ok(self, msg):
         """ Process a reply for a successful execution request.
         """
         payload = msg['content']['payload']
         for item in payload:
             if not self._process_execute_payload(item):
                 warning = 'Warning: received unknown payload of type %s'
                 print(warning % repr(item['source']))
 
     def _process_execute_payload(self, item):
         """ Process a single payload item from the list of payload items in an
             execution reply. Returns whether the payload was handled.
         """
         # The basic FrontendWidget doesn't handle payloads, as they are a
         # mechanism for going beyond the standard Python interpreter model.
         return False
 
     def _show_interpreter_prompt(self):
         """ Shows a prompt for the interpreter.
         """
         self._show_prompt('>>> ')
 
     def _show_interpreter_prompt_for_reply(self, msg):
         """ Shows a prompt for the interpreter given an 'execute_reply' message.
         """
         self._show_interpreter_prompt()
 
     #------ Signal handlers ----------------------------------------------------
 
     def _document_contents_change(self, position, removed, added):
         """ Called whenever the document's content changes. Display a call tip
             if appropriate.
         """
         # Calculate where the cursor should be *after* the change:
         position += added
 
         document = self._control.document()
         if position == self._get_cursor().position():
             self._call_tip()
 
     #------ Trait default initializers -----------------------------------------
 
     def _banner_default(self):
         """ Returns the standard Python banner.
         """
         banner = 'Python %s on %s\nType "help", "copyright", "credits" or ' \
             '"license" for more information.'
         return banner % (sys.version, sys.platform)