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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 decode_unicode_string(string):
 """ Decode string encoded by `unicode_string` """

    if string.startswith('[BASE64-DATA]') and string.endswith('[/BASE64-DATA]'):
        return base64.b64decode(string[len('[BASE64-DATA]'):-len('[/BASE64-DATA]')])
    return string