> Version 3 of my patch:
>  - Add PYTHONHASHSEED environment variable to get a fixed seed or to
> disable the randomized hash function (PYTHONHASHSEED=0)
>  - Add tests on the randomized hash function
>  - Add more tests on os.urandom()

You forgot random.c.

+        PyErr_SetString(PyExc_RuntimeError, "Fail to generate random
bytes");

I would put an OSError and preserve the errno.

+    def test_null_hash(self):
+        # PYTHONHASHSEED=0 disables the randomized hash
+        self.assertEqual(self.get_hash("abc", 0), -1600925533)
+
+    def test_fixed_hash(self):
+        # test a fixed seed for the randomized hash
+        self.assertEqual(self.get_hash("abc", 42), -206076799)

This is portable on both 32-bit and 64-bit builds?