FIX: correct handling of built-ins

IPython/core/completer.py

@@ -841,14 +841,18 b' class IPCompleter(Completer):'
                 call_obj = obj.__call__
         ret += self._default_arguments_from_docstring(
                  getattr(call_obj, '__doc__', ''))
-        try:
+
             if PY3:
                 _keepers = (inspect.Parameter.KEYWORD_ONLY,
                             inspect.Parameter.POSITIONAL_OR_KEYWORD)
+            try:
                 sig = inspect.signature(call_obj)
                 ret.extend(k for k, v in sig.parameters.items() if
                            v.kind in _keepers)
+            except ValueError:
+                pass
             else:
+            try:
                 args, _, _1, defaults = inspect.getargspec(call_obj)
                 if defaults:
                     ret += args[-len(defaults):]