code: def send_formdata(self, request, headers=None, content=None, **config):
          
          request.headers = headers
          request.add_formdata(content)
          return self.send(request, **config)
docs: Send data as a multipart form-data request.
          We only deal with file-like objects or strings at this point.
          The requests is not yet streamed.
  
          This method is deprecated, and shouldn't be used anymore.
  
          :param ClientRequest request: The request object to be sent.
          :param dict headers: Any headers to add to the request.
          :param dict content: Dictionary of the fields of the formdata.
          :param config: Any specific config overrides.