call = re.compile(r"""
     superLibFunc  # name of function to match 
     \s*           # possible whitespace
     \(            # parenthesis before argument list
     \s*           # possible whitespace
     (?P<arg1>%s)  # first argument plus optional whitespace
     ,             # comma between the arguments
     \s*           # possible whitespace
     (?P<arg2>%s)  # second argument plus optional whitespace
     \)            # closing parenthesis
     """ % (arg,arg), re.VERBOSE)

# the substitution command:
filestr = call.sub(r"superLibFunc(\g<arg2>, 
                   \g<arg1>)",filestr)