human
Here's a good function header given the following:
I wrote the below code

    def check_candidate(path, directory=None):
        'Auxilliary    function    that    checks    whether    a    particular\n                                path    is    a    good    candidate.\n\n                                '
        candidate = os.path.join(path, 'share', 'ivre')
        if (directory is not None):
            candidate = os.path.join(candidate, directory)
        try:
            if stat.S_ISDIR(os.stat(candidate).st_mode):
                return candidate
        except OSError:
            pass
    if __file__.startswith('/'):
        path = '/'
        for elt in __file__.split(os.path.sep)[1:]:
            if (elt in ['lib', 'lib32', 'lib64']):
                candidate = check_candidate(path, directory=directory)
                if (candidate is not None):
                    return candidate
            path = os.path.join(path, elt)
    for path in ['/usr', '/usr/local', '/opt', '/opt/ivre']:
        candidate = check_candidate(path, directory=directory)
        if (candidate is not None):
            return candidate

What's a good function header?
assistant
#Here's a good function header.

def guess_prefix(directory=None):