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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 add_header(self, header, value):
 # type: (str, str) -> None """Add a persistent header - this header will be applied to all requests sent during the current client session. .. deprecated:: 0.5.0 Use config.headers instead :param str header: The header name. :param str value: The header value. """

        warnings.warn("Private attribute _client.add_header is deprecated. Use config.headers instead.",
                      DeprecationWarning)
        self.config.headers[header] = value