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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 filename_to_date(filename, datefmt=None):
 """ Return a datetime from a file name. :param datefmt: strftime format string, ``settings.DATE_FORMAT`` is used if is ``None`` :type datefmt: ``str`` or ``NoneType`` :returns: Date guessed or nothing if no date found :rtype: ``datetime.datetime`` or ``NoneType`` """

    datefmt = datefmt or settings.DATE_FORMAT
    datestring = filename_to_datestring(filename, datefmt)
    if datestring is not None:
        return datetime.strptime(datestring, datefmt)