diff -r f903cf864191 Doc/library/inspect.rst
--- a/Doc/library/inspect.rst	Thu Apr 18 19:37:06 2013 +0200
+++ b/Doc/library/inspect.rst	Thu Apr 18 21:59:26 2013 +0100
@@ -340,7 +340,16 @@
 
    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). An :exc:`OSError` is raised
+   if the source code cannot be retrieved, and a :exc:`TypeError` is raised if
+   the object is a built-in module, class or function.
+
+   .. versionchanged:: 3.4
+      :exc:`OSError` is raised if the source code cannot be retrieved, rather
+      than returning ``None``.
+
+      :exc:`TypeError` is raised if the object is a built-in module, class or
+      function.
 
 
 .. function:: getfile(object)
diff -r f903cf864191 Lib/inspect.py
--- a/Lib/inspect.py	Thu Apr 18 19:37:06 2013 +0200
+++ b/Lib/inspect.py	Thu Apr 18 21:59:26 2013 +0100
@@ -610,12 +610,10 @@
 def getcomments(object):
     """Get lines of comments immediately preceding an object's source code.
 
-    Returns None when source can't be found.
+    An OSError is raised if the source code cannot be retrieved. A TypeError is
+    raised if object is a built-in module, class or function.
     """
-    try:
-        lines, lnum = findsource(object)
-    except (OSError, TypeError):
-        return None
+    lines, lnum = findsource(object)
 
     if ismodule(object):
         # Look for a comment block at the top of the file.
diff -r f903cf864191 Lib/test/test_inspect.py
--- a/Lib/test/test_inspect.py	Thu Apr 18 19:37:06 2013 +0200
+++ b/Lib/test/test_inspect.py	Thu Apr 18 21:59:26 2013 +0100
@@ -2,6 +2,7 @@
 import sys
 import types
 import unittest
+import unittest.mock
 import inspect
 import linecache
 import datetime
@@ -259,6 +260,11 @@
     def test_getcomments(self):
         self.assertEqual(inspect.getcomments(mod), '# line 1\n')
         self.assertEqual(inspect.getcomments(mod.StupidGit), '# line 20\n')
+        self.assertRaisesRegex(TypeError, 'built-in',
+                               inspect.getcomments, list)
+        # If the source file is unavailable, should raise OSError.
+        with unittest.mock.patch('inspect.getsourcefile', return_value=''):
+            self.assertRaises(OSError, inspect.getcomments, mod)
 
     def test_getmodule(self):
         # Check actual module
@@ -277,6 +283,11 @@
     def test_getsource(self):
         self.assertSourceEqual(git.abuse, 29, 39)
         self.assertSourceEqual(mod.StupidGit, 21, 46)
+        self.assertRaisesRegex(TypeError, 'built-in',
+                               inspect.getcomments, list)
+        # If the source file is unavailable, should raise OSError.
+        with unittest.mock.patch('inspect.getsourcefile', return_value=""):
+            self.assertRaises(OSError, inspect.getcomments, mod)
 
     def test_getsourcefile(self):
         self.assertEqual(normcase(inspect.getsourcefile(mod.spam)), modfile)