'Specify quality of service.
The client can request that messages should be sent in
advance so that when the client finishes processing a message,
the following message is already held locally, rather than needing
to be sent down the channel. Prefetching gives a performance
improvement.
The prefetch window is Ignored if the :attr:`no_ack` option is set.
Arguments:
prefetch_size (int): Specify the prefetch window in octets.
The server will send a message in advance if it is equal to
or smaller in size than the available prefetch size (and
also falls within other prefetch limits). May be set to zero,
meaning "no specific limit", although other prefetch limits
may still apply.
prefetch_count (int): Specify the prefetch window in terms of
whole messages.
apply_global (bool): Apply new settings globally on all channels.'

def qos(self, prefetch_size=0, prefetch_count=0, apply_global=False):

    return self.channel.basic_qos(prefetch_size, prefetch_count, apply_global)
