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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 fix_url(url):
 """ Strip whitespace characters from the beginning and the end of the url and add a default scheme. """

    if url is None:
        return None

    url = url.strip()

    if url and not urlparse(url).scheme:
        url = "http://" + url

    return url