A function call used as a default parameter value is evaluated
once when the module code is first read in. However, the
os.getcwd() function might give different results at run time
than at module reading time.

This replaces those default param values with None, and has the
function bodies call os.getcwd() if the param happens to be None.
See also

http://docs.python.org/reference/compound_stmts.html#function-definitions