I just installed Python 3.0a4 from source on an Ubuntu system and noticed that it doesn't seem to set the distutils.sysconfig config var: "SO":

```
vagrant@ubuntu:~/src/Python-3.4.0a4$ python3.4
Python 3.4.0a4 (default, Nov 11 2013, 17:11:59)
[GCC 4.6.3] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from distutils import sysconfig
>>> sysconfig.get_config_var("SO")
>>> sysconfig.get_config_var("SO") is None
True
```

This worked fine for me in Python 3.3:

```
vagrant@ubuntu:~/src/Python-3.4.0a4$ python3.3
Python 3.3.2 (default, May 16 2013, 18:32:41)
[GCC 4.6.3] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from distutils import sysconfig
>>> sysconfig.get_config_var("SO")
'.so'
```