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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 compose_tree_url(tree, issn_url=False):
 """ Compose full url for given `tree`, with protocol, server's address and port. Args: tree (obj):
 :class:`.Tree` instance. issn_url (bool, default False):
 Compose URL using ISSN. Returns: str: URL of the tree """

    url = compose_tree_path(tree, issn_url)

    if WEB_PORT == 80:
        return "%s://%s%s" % (_PROTOCOL, WEB_ADDR, url)

    return "%s://%s:%d%s" % (_PROTOCOL, WEB_ADDR, WEB_PORT, url)