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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def sink_pubsub(client, to_delete):
 """Sink log entries to pubsub."""

    topic = _sink_pubsub_setup(client)
    to_delete.append(topic)
    SINK_NAME = "robots-pubsub-%d" % (_millis(),)
    FILTER = "logName:apache-access AND textPayload:robot"
    UPDATED_FILTER = "textPayload:robot"

    # [START sink_pubsub_create]
    DESTINATION = "pubsub.googleapis.com/%s" % (topic.full_name,)
    sink = client.sink(SINK_NAME, filter_=FILTER, destination=DESTINATION)
    assert not sink.exists()  # API call
    sink.create()  # API call
    assert sink.exists()  # API call
    # [END sink_pubsub_create]
    to_delete.insert(0, sink)  # delete sink before topic

    # [START client_list_sinks]
    for sink in client.list_sinks():  # API call(s)
        do_something_with(sink)
    # [END client_list_sinks]

    # [START sink_reload]
    existing_sink = client.sink(SINK_NAME)
    existing_sink.reload()
    # [END sink_reload]
    assert existing_sink.filter_ == FILTER
    assert existing_sink.destination == DESTINATION

    # [START sink_update]
    existing_sink.filter_ = UPDATED_FILTER
    existing_sink.update()
    # [END sink_update]
    existing_sink.reload()
    assert existing_sink.filter_ == UPDATED_FILTER

    # [START sink_delete]
    sink.delete()
    # [END sink_delete]
    to_delete.pop(0)