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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 absolute_url (base_url, base_ref, parent_url):
 """ Search for the absolute url to detect the link type. This does not join any url fragments together! @param base_url: base url from a link tag @type base_url: string or None @param base_ref: base url from <base> tag @type base_ref: string or None @param parent_url: url of parent document @type parent_url: string or None """

    if base_url and urlutil.url_is_absolute(base_url):
        return base_url
    elif base_ref and urlutil.url_is_absolute(base_ref):
        return base_ref
    elif parent_url and urlutil.url_is_absolute(parent_url):
        return parent_url
    return u""