Causal Consistency Examples for the Manual

   # Start Causal Consistency Example 1

    with client.start_session(causal_consistency=True) as s1:

        current_date = datetime.datetime.today()

        items = client.get_database('test', 

                                    read_concern=ReadConcern("majority"),

                                    write_concern=WriteConcern(w='majority', wtimeout=1000)).items

        items.update_one({'sku': "111", 'end': None }, {'$set': {'end': current_date}}, session=s1)

        items.insert_one({'sku': "nuts-111", 'name': "Pecans", 'start': current_date}, session=s1)

   # End Causal Consistency Example 1

   # Start Causal Consistency Example 2

    with client.start_session(causal_consistency=True) as s2:

        s2.advance_cluster_time(s1.cluster_time)

        s2.advance_operation_time(s1.operation_time)

        items = client.get_database('test', read_preference=ReadPreference.SECONDARY,

                                    read_concern=ReadConcern("majority"),

                                    write_concern=WriteConcern(w='majority', wtimeout=1000)).items

        for item in items.find({'end': None}, session=s2):

            print(item)

   # End Causal Consistency Example 2