is
        not known, and the port is not provided, this attribute will
        be set to None.

        >>> URL.from_text(u'http://example.com/pa/th').port
        80
        >>> URL.from_text(u'foo://example.com/pa/th').port
        >>> URL.from_text(u'foo://example.com:8042/pa/th').port
        8042

        .. note::

           Per the standard, when the port is the same as the schemes
           default port, it will be omitted in the text URL.

        )