The filter() function does support a None argument in Py3.0.

Lib/test/test_py3kwarn.py

@@ -48,17 +48,6 @@ class TestPy3KWarnings(unittest.TestCase):
         with catch_warning() as w:
             self.assertWarning(cell0 < cell1, w, expected)
 
-    def test_filter(self):
-        from itertools import ifilter
-        from future_builtins import filter
-        expected = 'ifilter with None as a first argument is not supported '\
-                   'in 3.x.  Use a list comprehension instead.'
-
-        with catch_warning() as w:
-            self.assertWarning(ifilter(None, []), w, expected)
-        with catch_warning() as w:
-            self.assertWarning(filter(None, []), w, expected)
-
     def test_code_inequality_comparisons(self):
         expected = 'code inequality comparisons not supported in 3.x.'
         def f(x):

Modules/itertoolsmodule.c

@@ -2552,15 +2552,6 @@ ifilter_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
 	if (!PyArg_UnpackTuple(args, "ifilter", 2, 2, &func, &seq))
 		return NULL;
 
-	if (func == Py_None) {
-		if (Py_Py3kWarningFlag &&
-		    PyErr_Warn(PyExc_DeprecationWarning,
-			       "ifilter with None as a first argument "
-			       "is not supported in 3.x.  Use a list "
-			       "comprehension instead.") < 0)
-			return NULL;
-	}
-
 	/* Get iterator. */
 	it = PyObject_GetIter(seq);
 	if (it == NULL)

Python/bltinmodule.c

@@ -296,13 +296,6 @@ builtin_filter(PyObject *self, PyObject *args)
 		}
 
 		if (func == (PyObject *)&PyBool_Type || func == Py_None) {
-			if (Py_Py3kWarningFlag &&
-			    PyErr_Warn(PyExc_DeprecationWarning,
-				       "filter with None as a first argument "
-				       "is not supported in 3.x.  Use a list "
-				       "comprehension instead.") < 0)
-				return NULL;
-
 			ok = PyObject_IsTrue(item);
 		}
 		else {