ConfigParser doesn't prevent "manually" adding a section named DEFAULT;
however, doing so creates a duplicate, inaccessible [DEFAULT] section in
the config file:
----
>>> import sys, ConfigParser
>>> c = ConfigParser.ConfigParser()
>>> c.add_section('DEFAULT')
>>> c.write(sys.stdout)
[DEFAULT]

>>> c.set('DEFAULT', 'color', 'yellow')
>>> c.write(sys.stdout)
[DEFAULT]
color = yellow

[DEFAULT]

----
It seems that the correct thing to do would be to disallow
add_section('DEFAULT').