diff -r 64d9569b4e1f Doc/library/inspect.rst
--- a/Doc/library/inspect.rst	Sat Oct 12 01:41:49 2013 +0200
+++ b/Doc/library/inspect.rst	Sun Oct 13 11:40:45 2013 +0800
@@ -341,7 +341,9 @@
 
    Return in a single string any lines of comments immediately preceding the
    object's source code (for a class, function, or method), or at the top of the
-   Python source file (if the object is a module).
+   Python source file (if the object is a module). If the object's source code
+   is unavailable, return ``None``. This could happen if the object has been
+   defined in C or interactive shell.
 
 
 .. function:: getfile(object)
diff -r 64d9569b4e1f Lib/test/test_inspect.py
--- a/Lib/test/test_inspect.py	Sat Oct 12 01:41:49 2013 +0200
+++ b/Lib/test/test_inspect.py	Sun Oct 13 11:40:45 2013 +0800
@@ -10,14 +10,18 @@
 import shutil
 import functools
 import importlib
+import textwrap
+import imp
 from os.path import normcase
 try:
     from concurrent.futures import ThreadPoolExecutor
 except ImportError:
     ThreadPoolExecutor = None
 
-from test.support import run_unittest, TESTFN, DirsOnSysPath
-from test.script_helper import assert_python_ok, assert_python_failure
+from test.support import run_unittest, TESTFN, DirsOnSysPath, unlink
+from test.script_helper import (assert_python_ok,
+                                assert_python_failure,
+                                make_script)
 from test import inspect_fodder as mod
 from test import inspect_fodder2 as mod2
 
@@ -280,8 +284,26 @@
                          'An\nindented\ndocstring.')
 
     def test_getcomments(self):
-        self.assertEqual(inspect.getcomments(mod), '# line 1\n')
-        self.assertEqual(inspect.getcomments(mod.StupidGit), '# line 20\n')
+        source_content = textwrap.dedent("""\
+            # line 1
+            'A module docstring.'
+
+            # line 20
+            class StupidGit:
+                pass
+            """)
+        source_file = TESTFN + '.py'
+        self.addCleanup(unlink, source_file)
+        make_script('', TESTFN, source_content)
+        spam = imp.load_source('spam', source_file)
+        self.assertEqual(inspect.getcomments(spam), '# line 1\n')
+        self.assertEqual(inspect.getcomments(spam.StupidGit), '# line 20\n')
+        # If the source file is unavailable, it should return None.
+        unlink(source_file)
+        del linecache.cache[source_file]
+        self.assertIsNone(inspect.getcomments(spam))
+        # If the object has been defined in C, it should return None.
+        self.assertIsNone(inspect.getcomments(list))
 
     def test_getmodule(self):
         # Check actual module