def upload(self, fileobj, bucket, key, extra_args=None, subscribers=None):
        if extra_args is None:
            extra_args = {}
        if subscribers is None:
            subscribers = {}
        callargs = CallArgs(
            bucket=bucket,
            key=key,
            fileobj=fileobj,
            extra_args=extra_args,
            subscribers=subscribers,
        )
        return self._submit_transfer("put_object", callargs)