org-babel-execute-src-block: No org-babel-execute function for python!

When evaluating the following block C-c C-c starting from emacs -Q

#+BEGIN_SRC python
a = 5

b = 16

print(a + b)
#+END_SRC

the error message from title appears

GNU Emacs 24.3.50.1 (i686-suse-linux-gnu, GTK+ Version 2.22.1) of 2013-02-20

Patch attached.