Added machinery to IPythonWidget for updating the previous prompt number.

IPython/frontend/qt/console/console_widget.py

@@ -214,11 +214,11 b' class ConsoleWidget(QtGui.QPlainTextEdit):'
 
             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)
+                    start_pos = self._prompt_pos
                 else:
+                    start_pos = cursor.position()
                     start_pos += len(self._continuation_prompt)
                 if shift_down and self._in_buffer(position):
                     self._set_selection(position, start_pos)
@@ -266,22 +266,7 b' class ConsoleWidget(QtGui.QPlainTextEdit):'
             make sense for a console widget.
         """
         cursor = self._get_end_cursor()
-        cursor.insertHtml(html)
-
-        # After appending HTML, the text document "remembers" the current
-        # formatting, which means that subsequent calls to 'appendPlainText'
-        # will be formatted similarly, a behavior that we do not want. To
-        # prevent this, we make sure that the last character has no formatting.
-        cursor.movePosition(QtGui.QTextCursor.Left, 
-                            QtGui.QTextCursor.KeepAnchor)
-        if cursor.selection().toPlainText().trimmed().isEmpty():
-            # If the last character is whitespace, it doesn't matter how it's
-            # formatted, so just clear the formatting.
-            cursor.setCharFormat(QtGui.QTextCharFormat())
-        else:
-            # Otherwise, add an unformatted space.
-            cursor.movePosition(QtGui.QTextCursor.Right)
-            cursor.insertText(' ', QtGui.QTextCharFormat())
+        self._insert_html(cursor, html)
 
     def appendPlainText(self, text):
         """ Reimplemented to not append text as a new paragraph, which doesn't
@@ -712,6 +697,27 b' class ConsoleWidget(QtGui.QPlainTextEdit):'
         cursor.setPosition(position)
         return cursor
 
+    def _insert_html(self, cursor, html):
+        """ Insert HTML using the specified cursor in such a way that future
+            formatting is unaffected.
+        """
+        cursor.insertHtml(html)
+
+        # After inserting HTML, the text document "remembers" the current
+        # formatting, which means that subsequent calls adding plain text
+        # will result in similar formatting, a behavior that we do not want. To
+        # prevent this, we make sure that the last character has no formatting.
+        cursor.movePosition(QtGui.QTextCursor.Left, 
+                            QtGui.QTextCursor.KeepAnchor)
+        if cursor.selection().toPlainText().trimmed().isEmpty():
+            # If the last character is whitespace, it doesn't matter how it's
+            # formatted, so just clear the formatting.
+            cursor.setCharFormat(QtGui.QTextCharFormat())
+        else:
+            # Otherwise, add an unformatted space.
+            cursor.movePosition(QtGui.QTextCursor.Right)
+            cursor.insertText(' ', QtGui.QTextCharFormat())
+
     def _prompt_started(self):
         """ Called immediately after a new prompt is displayed.
         """

IPython/frontend/qt/console/ipython_widget.py

@@ -30,6 +30,10 b' class IPythonWidget(FrontendWidget):'
         .out-prompt-number { color: red; font-weight: bold; }
     """
 
+    # Default prompts.
+    in_prompt = '<br/>In [<span class="in-prompt-number">%i</span>]: '
+    out_prompt = 'Out[<span class="out-prompt-number">%i</span>]: '
+
     #---------------------------------------------------------------------------
     # 'QObject' interface
     #---------------------------------------------------------------------------
@@ -38,6 +42,7 b' class IPythonWidget(FrontendWidget):'
         super(IPythonWidget, self).__init__(parent)
 
         # Initialize protected variables.
+        self._previous_prompt_blocks = []
         self._prompt_count = 0
 
         # Set a default stylesheet.
@@ -64,17 +69,29 b' class IPythonWidget(FrontendWidget):'
     def _show_interpreter_prompt(self):
         """ Reimplemented for IPython-style prompts.
         """
+        # Update old prompt numbers if necessary.
+        previous_prompt_number = self._prompt_count
+        if previous_prompt_number != self._prompt_count:
+            for i, (block, length) in enumerate(self._previous_prompt_blocks):
+                if block.isValid():
+                    cursor = QtGui.QTextCursor(block)
+                    cursor.movePosition(QtGui.QTextCursor.Right,
+                                        QtGui.QTextCursor.KeepAnchor, length-1)
+                    if i == 0:
+                        prompt = self._make_in_prompt(previous_prompt_number)
+                    else:
+                        prompt = self._make_out_prompt(previous_prompt_number)
+                    self._insert_html(cursor, prompt)
+        self._previous_prompt_blocks = []
+
+        # Show a new prompt.
         self._prompt_count += 1
-        prompt_template = '<span class="in-prompt">%s</span>'
-        prompt_body = '<br/>In [<span class="in-prompt-number">%i</span>]: '
-        prompt = (prompt_template % prompt_body) % self._prompt_count
-        self._show_prompt(prompt, html=True)
+        self._show_prompt(self._make_in_prompt(self._prompt_count), html=True)
+        self._save_prompt_block()
 
         # Update continuation prompt to reflect (possibly) new prompt length.
-        cont_prompt_chars = '...: '
-        space_count = len(self._prompt.lstrip()) - len(cont_prompt_chars)
-        cont_prompt_body = '&nbsp;' * space_count + cont_prompt_chars
-        self._continuation_prompt_html = prompt_template % cont_prompt_body
+        self._set_continuation_prompt(
+            self._make_continuation_prompt(self._prompt), html=True)
 
     #------ Signal handlers ----------------------------------------------------
 
@@ -96,10 +113,9 b' class IPythonWidget(FrontendWidget):'
     def _handle_pyout(self, omsg):
         """ Reimplemented for IPython-style "display hook".
         """
-        prompt_template = '<span class="out-prompt">%s</span>'
-        prompt_body = 'Out[<span class="out-prompt-number">%i</span>]: '
-        prompt = (prompt_template % prompt_body) % self._prompt_count
-        self.appendHtml(prompt)
+        self.appendHtml(self._make_out_prompt(self._prompt_count))
+        self._save_prompt_block()
+        
         self.appendPlainText(omsg['content']['data'] + '\n')
 
     #---------------------------------------------------------------------------
@@ -135,6 +151,38 b' class IPythonWidget(FrontendWidget):'
         else:
             self._highlighter.set_style(syntax_style)
 
+    #---------------------------------------------------------------------------
+    # 'IPythonWidget' protected interface
+    #---------------------------------------------------------------------------
+
+    def _make_in_prompt(self, number):
+        """ Given a prompt number, returns an HTML In prompt.
+        """
+        body = self.in_prompt % number
+        return '<span class="in-prompt">%s</span>' % body
+
+    def _make_continuation_prompt(self, prompt):
+        """ Given a plain text version of an In prompt, returns an HTML
+            continuation prompt.
+        """
+        end_chars = '...: '
+        space_count = len(prompt.lstrip('\n')) - len(end_chars)
+        body = '&nbsp;' * space_count + end_chars
+        return '<span class="in-prompt">%s</span>' % body
+        
+    def _make_out_prompt(self, number):
+        """ Given a prompt number, returns an HTML Out prompt.
+        """
+        body = self.out_prompt % number
+        return '<span class="out-prompt">%s</span>' % body
+
+    def _save_prompt_block(self):
+        """ Assuming a prompt has just been written at the end of the buffer,
+            store the QTextBlock that contains it and its length.
+        """
+        block = self.document().lastBlock()
+        self._previous_prompt_blocks.append((block, block.length()))
+
 
 if __name__ == '__main__':
     from IPython.frontend.qt.kernelmanager import QtKernelManager