How to use the treq.multipart.MultiPartProducer function in treq

if files:
            # If the files keyword is present we will issue a
            # multipart/form-data request as it suits better for cases
            # with files and/or large objects.
            files = list(_convert_files(files))
            boundary = str(uuid.uuid4()).encode('ascii')
            headers.setRawHeaders(
                b'content-type', [
                    b'multipart/form-data; boundary=' + boundary])
            if data:
                data = _convert_params(data)
            else:
                data = []

            bodyProducer = multipart.MultiPartProducer(
                data + files, boundary=boundary)
        elif data:
            # Otherwise stick to x-www-form-urlencoded format
            # as it's generally faster for smaller requests.
            if isinstance(data, (dict, list, tuple)):
                headers.setRawHeaders(
                    b'content-type', [b'application/x-www-form-urlencoded'])
                data = urlencode(data, doseq=True)
            bodyProducer = self._data_to_body_producer(data)
        elif has_json:
            # If data is sent as json, set Content-Type as 'application/json'
            headers.setRawHeaders(
                b'content-type', [b'application/json; charset=UTF-8'])
            content = kwargs['json']
            json = json_dumps(content, separators=(u',', u':')).encode('utf-8')
            bodyProducer = self._data_to_body_producer(json)

files = kwargs.get('files')
        if files:
            # If the files keyword is present we will issue a
            # multipart/form-data request as it suits better for cases
            # with files and/or large objects.
            files = list(_convert_files(files))
            boundary = uuid.uuid4()
            headers.setRawHeaders(
                'content-type', [
                    'multipart/form-data; boundary=%s' % (boundary,)])
            if data:
                data = _convert_params(data)
            else:
                data = []

            bodyProducer = multipart.MultiPartProducer(
                data + files, boundary=boundary)
        elif data:
            # Otherwise stick to x-www-form-urlencoded format
            # as it's generally faster for smaller requests.
            if isinstance(data, (dict, list, tuple)):
                headers.setRawHeaders(
                    'content-type', ['application/x-www-form-urlencoded'])
                data = urlencode(data, doseq=True)
            bodyProducer = IBodyProducer(data)

        wrapped_agent = self._agent

        if kwargs.get('allow_redirects', True):
            wrapped_agent = RedirectAgent(wrapped_agent)

        wrapped_agent = ContentDecoderAgent(wrapped_agent,