make getting filename python2 compatible

Author: amueller

Diff for: numpydoc/numpydoc.py

@@ -116,7 +116,10 @@ def mangle_signature(app, what, name, obj, options, sig, retann):
     try:
         doc = SphinxDocString(pydoc.getdoc(obj))
     except ValueError as e:
-        filename = obj.__code__.co_filename
+        try:
+            filename = inspect.getsourcefile(obj)
+        except TypeError:
+            filename = None
         raise ValueError(str(e) + " in {}:{}".format(filename, name))
     sig = doc['Signature'] or getattr(obj, '__text_signature__', None)
     if sig: