The FrontendWidget now performs tab-completion more aggressively.

IPython/frontend/qt/console/console_widget.py

@@ -641,8 +641,10 b' class ConsoleWidget(QtGui.QWidget):'
             elif key == QtCore.Qt.Key_Tab:
                 if self._reading:
                     intercepted = False
+                elif not self._tab_pressed():
+                    intercepted = True
                 else:
-                    intercepted = not self._tab_pressed()
+                    intercepted = not self._in_buffer()
 
             elif key == QtCore.Qt.Key_Left:
                 intercepted = not self._in_buffer(position - 1)
@@ -968,11 +970,15 b' class ConsoleWidget(QtGui.QWidget):'
             cursor.endEditBlock()
             self._control.setTextCursor(cursor)
 
-    def _in_buffer(self, position):
-        """ Returns whether the given position is inside the editing region.
+    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()
-        cursor.setPosition(position)
+        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:
@@ -987,13 +993,12 b' class ConsoleWidget(QtGui.QWidget):'
         """ Ensures that the cursor is inside the editing region. Returns
             whether the cursor was moved.
         """
-        cursor = self._control.textCursor()
-        if self._in_buffer(cursor.position()):
-            return False
-        else:
+        moved = not self._in_buffer()
+        if moved:
+            cursor = self._control.textCursor()
             cursor.movePosition(QtGui.QTextCursor.End)
             self._control.setTextCursor(cursor)
-            return True
+        return moved
         
     def _page(self, text):
         """ Displays text using the pager if it exceeds the height of the

IPython/frontend/qt/console/frontend_widget.py

@@ -148,9 +148,16 b' class FrontendWidget(HistoryConsoleWidget, BaseFrontendMixin):'
         """ Called when the tab key is pressed. Returns whether to continue
             processing the event.
         """
-        self._keep_cursor_in_buffer()
-        cursor = self._get_cursor()
-        return not self._complete()
+        # 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