Index: Lib/doctest.py
===================================================================
--- Lib/doctest.py	(revision 67009)
+++ Lib/doctest.py	(working copy)
@@ -815,17 +815,6 @@
         elif module is None:
             module = inspect.getmodule(obj)
 
-        # Read the module's source code.  This is used by
-        # DocTestFinder._find_lineno to find the line number for a
-        # given object's docstring.
-        try:
-            file = inspect.getsourcefile(obj) or inspect.getfile(obj)
-            source_lines = linecache.getlines(file)
-            if not source_lines:
-                source_lines = None
-        except TypeError:
-            source_lines = None
-
         # Initialize globals, and merge in extraglobs.
         if globs is None:
             if module is None:
@@ -837,6 +826,20 @@
         if extraglobs is not None:
             globs.update(extraglobs)
 
+        # Read the module's source code.  This is used by
+        # DocTestFinder._find_lineno to find the line number for a
+        # given object's docstring.
+        try:
+            if hasattr(obj, '__file__') and obj.__file__ is None and module:
+                file = module.__name__ + '.py'
+            else:
+                file = inspect.getsourcefile(obj) or inspect.getfile(obj)
+            source_lines = linecache.getlines(file, globs)
+            if not source_lines:
+                source_lines = None
+        except TypeError:
+            source_lines = None
+
         # Recursively expore `obj`, extracting DocTests.
         tests = []
         self._find(tests, obj, name, module, source_lines, globs, {})
@@ -961,7 +964,7 @@
         if module is None:
             filename = None
         else:
-            filename = getattr(module, '__file__', module.__name__)
+            filename = getattr(module, '__file__', None) or module.__name__
             if filename[-4:] in (".pyc", ".pyo"):
                 filename = filename[:-1]
         return self._parser.get_doctest(docstring, globs, name,