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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def pathjoin(*parts, **kvs):
    '''join path parts into a path; in case url is not none, use that, too'''
    url = kvs.pop('url', '/')
    url = url + '/' + '/'.join(parts)
    url = normalize_url(url)
    return url