(See Google Group )

With the Python pubsub package v 0.39.0, a simple call to pubsub_v1.SubscriberClient() gives warnings from deep in Google code

             
 publisher/client.py:89: PendingDeprecationWarning: The `channel` argument is deprecated; use `transport` instead.
  ...
  subscriber/client.py:83: PendingDeprecationWarning: The `channel` argument is deprecated; use `transport` instead.
  ...

This apparently incorrect channel is created inside Google code, e.g. google.cloud.pubsub_v1.subscriber.client.Client#__init__

Although keeping ahead of deprecation can be challenging, Google's own code should avoid warnings and do whatever Google says is the official way.