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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 _pfp__build(self, stream=None, save_offset=False):
 """Build the String field :stream: TODO :returns: TODO """

        if stream is not None and save_offset:
            self._pfp__offset = stream.tell()

        data = self._pfp__value + utils.binary("\x00")
        if stream is None:
            return data
        else:
            stream.write(data)
            return len(data)