boto3 query using KeyConditionExpression

Please change the ExpressionAttributeValues as mentioned below.

ExpressionAttributeValues={':cihan': 'cihan'}

In current versions of boto3 (1.9.128) the query mentioned in the question asked works fine, and nothing else apart from that is working now, the query mentioned below worked for me:-

dynamo_client.query( KeyConditionExpression='campaign_id = :201906', ExpressionAttributeValues={':201906': {'S': '201906'}} )