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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 dt_from_header(date_str):
 """Try various RFC conversions to ``datetime`` or return ``None``. :param date_str: Date string. :type date_str: ``string`` :return: Date time. :rtype: :class:`datetime.datetime` or ``None`` """

    convert_fns = (
        dt_from_rfc8601,
        dt_from_rfc1123,
    )

    for convert_fn in convert_fns:
        try:
            return convert_fn(date_str)
        except ValueError:
            pass

    return None