code: def write(self, buf):
          
          if not isinstance(buf, six.binary_type):
              raise TypeError('buf: must be a bytes instance')
          # Be careful not to write zero-length chunks as they indicate the end of a body.
          if len(buf) == 0:
              return
          if self._content_length and self._bytes_written > self._content_length:
              raise RuntimeError('wrote too many bytes ({} > {})'
                                      .format(self._bytes_written, self._content_length))
          self._bytes_written += len(buf)
          if self._chunked:
              buf = create_chunk(buf)
          self._protocol.writer.write(buf)
docs: Write *buf* to the request body.