It checks if parameter has a value. If it does it prepends a space. If not it returns an empty string.
$ python
Python 2.7.2 (default, Oct 11 2012, 20:14:37)
[GCC 4.2.1 Compatible Apple Clang 4.0 (tags/Apple/clang-418.0.60)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> foo = 'bar'
>>> foo and (" " + foo) or ""
' bar'
