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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 ext_from_filename(filename):
 """ Scan a filename for it's extension. :param filename: string of the filename :return: the extension off the end (empty string if it can't find one) """

    try:
        base, ext = filename.lower().rsplit(".", 1)
    except ValueError:
        return ''
    ext = ".{0}".format(ext)
    all_exts = [x.extension for x in chain(magic_header_array,
                                           magic_footer_array)]

    if base[-4:].startswith("."):
        # For double extensions like like .tar.gz
        long_ext = base[-4:] + ext
        if long_ext in all_exts:
            return long_ext
    return ext