First cut at safe appending in the Qt console.

IPython/frontend/qt/console/console_widget.py

@@ -718,36 +718,46 b' class ConsoleWidget(Configurable, QtGui.QWidget):'
     # 'ConsoleWidget' protected interface
     #--------------------------------------------------------------------------
 
-    def _append_html(self, html):
-        """ Appends html at the end of the console buffer.
+    def _append_custom(self, insert, input, before_prompt=False):
+        """ 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.
         """
-        cursor = self._get_end_cursor()
-        self._insert_html(cursor, html)
+        # Determine where to insert the content.
+        cursor = self._control.textCursor()
+        if before_prompt and not self._executing:
+            cursor.setPosition(self._prompt_pos)
+            cursor.movePosition(QtGui.QTextCursor.Left, n=len(self._prompt))
+        else:
+            cursor.movePosition(QtGui.QTextCursor.End)
+        start_pos = cursor.position()
 
-    def _append_html_fetching_plain_text(self, html):
-        """ Appends 'html', then returns the plain text version of it.
-        """
-        cursor = self._get_end_cursor()
-        return self._insert_html_fetching_plain_text(cursor, html)
+        # Perform the insertion.
+        result = insert(cursor, input)
+
+        # 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 not self._executing:
+            self._prompt_pos += cursor.position() - start_pos
+            
+        return result
 
-    def _append_plain_text(self, text):
-        """ Appends plain text at the end of the console buffer, processing
-            ANSI codes if enabled.
+    def _append_html(self, html, before_prompt=False):
+        """ Appends HTML at the end of the console buffer.
         """
-        cursor = self._get_end_cursor()
-        self._insert_plain_text(cursor, text)
+        self._append_custom(self._insert_html, html, before_prompt)
 
-    def _append_plain_text_keeping_prompt(self, text):
-        """ Writes 'text' after the current prompt, then restores the old prompt
-            with its old input buffer.
+    def _append_html_fetching_plain_text(self, html, before_prompt=False):
+        """ Appends HTML, then returns the plain text version of it.
         """
-        input_buffer = self.input_buffer
-        self._append_plain_text('\n')
-        self._prompt_finished()
+        return self._append_custom(self._insert_html_fetching_plain_text,
+                                   html, before_prompt)
 
-        self._append_plain_text(text)
-        self._show_prompt()
-        self.input_buffer = input_buffer
+    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_text_completion(self):
         """ If text completion is progress, cancel it.

IPython/frontend/qt/console/frontend_widget.py

@@ -372,14 +372,8 b' class FrontendWidget(HistoryConsoleWidget, BaseFrontendMixin):'
         """ Handle display hook output.
         """
         if not self._hidden and self._is_from_this_session(msg):
-            data = msg['content']['data']
-            if isinstance(data, basestring):
-                # plaintext data from pure Python kernel
-                text = data
-            else:
-                # formatted output from DisplayFormatter (IPython kernel)
-                text = data.get('text/plain', '')
-            self._append_plain_text(text + '\n')
+            text = msg['content']['data']
+            self._append_plain_text(text + '\n', before_prompt=True)
 
     def _handle_stream(self, msg):
         """ Handle stdout, stderr, and stdin.
@@ -390,7 +384,7 b' class FrontendWidget(HistoryConsoleWidget, BaseFrontendMixin):'
             # widget's tab width.
             text = msg['content']['data'].expandtabs(8)
             
-            self._append_plain_text(text)
+            self._append_plain_text(text, before_prompt=True)
             self._control.moveCursor(QtGui.QTextCursor.End)
 
     def _handle_shutdown_reply(self, msg):

IPython/frontend/qt/console/ipython_widget.py

@@ -62,16 +62,16 b' class IPythonWidget(FrontendWidget):'
     editor = Unicode(default_editor, config=True,
         help="""
         A command for invoking a system text editor. If the string contains a
-        {filename} format specifier, it will be used. Otherwise, the filename will
-        be appended to the end the command.
+        {filename} format specifier, it will be used. Otherwise, the filename
+        will be appended to the end the command.
         """)
 
     editor_line = Unicode(config=True,
         help="""
         The editor command to use when a specific line number is requested. The
         string should contain two format specifiers: {line} and {filename}. If
-        this parameter is not specified, the line number option to the %edit magic
-        will be ignored.
+        this parameter is not specified, the line number option to the %edit
+        magic will be ignored.
         """)
 
     style_sheet = Unicode(config=True,
@@ -85,8 +85,9 b' class IPythonWidget(FrontendWidget):'
 
     syntax_style = Str(config=True,
         help="""
-        If not empty, use this Pygments style for syntax highlighting. Otherwise,
-        the style sheet is queried for Pygments style information.
+        If not empty, use this Pygments style for syntax highlighting.
+        Otherwise, the style sheet is queried for Pygments style
+        information.
         """)
 
     # Prompts.
@@ -187,20 +188,20 b' class IPythonWidget(FrontendWidget):'
             prompt_number = content['execution_count']
             data = content['data']
             if data.has_key('text/html'):
-                self._append_plain_text(self.output_sep)
-                self._append_html(self._make_out_prompt(prompt_number))
+                self._append_plain_text(self.output_sep, True)
+                self._append_html(self._make_out_prompt(prompt_number), True)
                 html = data['text/html']
-                self._append_plain_text('\n')
-                self._append_html(html + self.output_sep2)
+                self._append_plain_text('\n', True)
+                self._append_html(html + self.output_sep2, True)
             elif data.has_key('text/plain'):
-                self._append_plain_text(self.output_sep)
-                self._append_html(self._make_out_prompt(prompt_number))
+                self._append_plain_text(self.output_sep, True)
+                self._append_html(self._make_out_prompt(prompt_number), True)
                 text = data['text/plain']
                 # If the repr is multiline, make sure we start on a new line,
                 # so that its lines are aligned.
                 if "\n" in text and not self.output_sep.endswith("\n"):
-                    self._append_plain_text('\n')
-                self._append_plain_text(text + self.output_sep2)
+                    self._append_plain_text('\n', True)
+                self._append_plain_text(text + self.output_sep2, True)
 
     def _handle_display_data(self, msg):
         """ The base handler for the ``display_data`` message.
@@ -216,19 +217,19 b' class IPythonWidget(FrontendWidget):'
             # representation.
             if data.has_key('text/html'):
                 html = data['text/html']
-                self._append_html(html)
+                self._append_html(html, before_prompt=True)
             elif data.has_key('text/plain'):
                 text = data['text/plain']
-                self._append_plain_text(text)
+                self._append_plain_text(text, before_prompt=True)
             # This newline seems to be needed for text and html output.
-            self._append_plain_text(u'\n')
+            self._append_plain_text(u'\n', before_prompt=True)
 
     def _started_channels(self):
         """ Reimplemented to make a history request.
         """
         super(IPythonWidget, self)._started_channels()
-        self.kernel_manager.shell_channel.history(hist_access_type='tail', n=1000)
-
+        self.kernel_manager.shell_channel.history(hist_access_type='tail',
+                                                  n=1000)
     #---------------------------------------------------------------------------
     # 'ConsoleWidget' public interface
     #---------------------------------------------------------------------------
@@ -413,8 +414,8 b' class IPythonWidget(FrontendWidget):'
             self.custom_edit_requested.emit(filename, line)
         elif not self.editor:
             self._append_plain_text('No default editor available.\n'
-            'Specify a GUI text editor in the `IPythonWidget.editor` configurable\n'
-            'to enable the %edit magic')
+            'Specify a GUI text editor in the `IPythonWidget.editor` '
+            'configurable to enable the %edit magic')
         else:
             try:
                 filename = '"%s"' % filename