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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 get_headers_from_signature(self, signature):
 """Returns a list of headers fields to sign. According to http://tools.ietf.org/html/draft-cavage-http-signatures-03 section 2.1.3, the headers are optional. If not specified, the single value of "Date" must be used. """

        match = self.SIGNATURE_HEADERS_RE.search(signature)
        if not match:
            return ['date']
        headers_string = match.group(1)
        return headers_string.split()