org-babel: Why isn't =:results value= working with (my) python?

[Scott May <bscottmay@yahoo.com>]

Using org-babel, the following example produces no output for me when I execute using C-c C-c:

#+begin_src python :results value
2 + 2
#+end_src

#+results:
: None

In my messages buffer I see the following:

: (Shell command succeeded with no output)

Now the equivalent emacs-lisp example does work:

#+begin_src emacs-lisp :results value
(+ 2 2)
#+end_src

#+results:
: 4

Furthermore, 

#+begin_src python :results output
print(2 + 2)
#+end_src

#+results:
: 4

works as expected.

Am I missing something obvious? Is the problem with my python setup, or perhaps org-babel-python?

I have tested this on both my Windows and Ubuntu setups. I am using org version 6.34trans.

Cheers,
Scott