diff -r 651aa21433ba Lib/rlcompleter.py
--- a/Lib/rlcompleter.py	Mon Feb 02 17:47:31 2015 -0500
+++ b/Lib/rlcompleter.py	Wed Feb 11 11:21:04 2015 +0100
@@ -36,10 +36,10 @@
 __all__ = ["Completer"]
 
 class Completer:
-    def __init__(self, namespace = None):
+    def __init__(self, namespace = None, tab_to_space_pos = None):
         """Create a new completer for the command line.
 
-        Completer([namespace]) -> completer instance.
+        Completer([namespace][, tab_to_space_pos]) -> completer instance.
 
         If unspecified, the default namespace where completions are performed
         is __main__ (technically, __main__.__dict__). Namespaces should be
@@ -49,6 +49,10 @@
         readline via the set_completer() call:
 
         readline.set_completer(Completer(my_namespace).complete)
+
+        If 'tab_to_space_pos' is set, it must be a function that
+        returns the current line position.  Tabs are then converted to
+        (up to) 4 spaces if there is nothing to complete.
         """
 
         if namespace and not isinstance(namespace, dict):
@@ -62,6 +66,7 @@
         else:
             self.use_main_ns = 0
             self.namespace = namespace
+        self.tab_to_space_pos = tab_to_space_pos
 
     def complete(self, text, state):
         """Return the next possible completion for 'text'.
@@ -74,7 +79,11 @@
             self.namespace = __main__.__dict__
 
         if state == 0:
-            if "." in text:
+            if len(text) == 0 and self.tab_to_space_pos:
+                pos = self.tab_to_space_pos()
+                num_spaces = 4 - (pos % 4)
+                self.matches = [' ' * num_spaces]
+            elif "." in text:
                 self.matches = self.attr_matches(text)
             else:
                 self.matches = self.global_matches(text)
@@ -158,7 +167,8 @@
 except ImportError:
     pass
 else:
-    readline.set_completer(Completer().complete)
+    _getpos = readline.get_endidx
+    readline.set_completer(Completer(tab_to_space_pos=_getpos).complete)
     # Release references early at shutdown (the readline module's
     # contents are quasi-immortal, and the completer function holds a
     # reference to globals).
diff -r 651aa21433ba Lib/test/test_rlcompleter.py
--- a/Lib/test/test_rlcompleter.py	Mon Feb 02 17:47:31 2015 -0500
+++ b/Lib/test/test_rlcompleter.py	Wed Feb 11 11:21:04 2015 +0100
@@ -65,6 +65,15 @@
                          ['egg.{}('.format(x) for x in dir(str)
                           if x.startswith('s')])
 
+    def test_tab_to_space_pos(self):
+        completer = rlcompleter.Completer(tab_to_space_pos=lambda: pos)
+        pos = 0
+        self.assertEqual(completer.complete('', 0), '    ')
+        pos = 41
+        self.assertEqual(completer.complete('', 0), '   ')
+        pos = 43
+        self.assertEqual(completer.complete('', 0), ' ')
+
 def test_main():
     support.run_unittest(TestRlcompleter)