DynamoDB - Collection of not "trivial" operations

append_element_to_list.py

#Append time to a list using face_id as key. Create list if it doesn't exist.

def log_event(face_id, similarity):
    now = datetime.datetime.now()

    create_dynamodb = dynamodb_events_table.update_item(
       Key={
            'FaceId': face_id,
            'Timestamp': str(now.date())
       },
        UpdateExpression="SET #time_name = list_append(if_not_exists(#time_name, :empty_list), :t),  Similarity = :s",
        ExpressionAttributeNames = {
           "#time_name": "Time",
        },
        ExpressionAttributeValues={
            ":t": [ str(now.time()) ],
            ":s": similarity,
            ":empty_list": []
        },
        ReturnValues="UPDATED_NEW"
    )

cfn_ddb_policy.yml

    DynamoDBLambdaFunctionRole: 
      Type: AWS::IAM::Role
      Properties: 
        AssumeRolePolicyDocument: 
          Version: '2012-10-17'
          Statement: 
          - Effect: Allow
            Principal: 
              Service: lambda.amazonaws.com
            Action: 
            - sts:AssumeRole
        Path: '/'
        ManagedPolicyArns:
          - arn:aws:iam::aws:policy/service-role/AWSLambdaVPCAccessExecutionRole
        Policies: 
        - PolicyName: LambdaCwlPolicy
          PolicyDocument: 
            Statement: 
            - Effect: Allow
              Action: 
              - logs:CreateLogGroup
              - logs:CreateLogStream
              - logs:PutLogEvents
              Resource: arn:aws:logs:*:*:*
        - PolicyName: DynamoDBPolicy
          PolicyDocument: 
            Statement: 
            - Effect: Allow
              Action: 
              - dynamodb:UpdateItem
              - dynamodb:Scan
              - dynamodb:Query
              - dynamodb:PutItem
              - dynamodb:GetItem
              - dynamodb:DeleteItem
              - dynamodb:BatchGetItem
              - dynamodb:BatchWriteItem
              Resource: 
                - !Sub arn:aws:dynamodb:${AWS::Region}:${AWS::AccountId}:table/${Table1}
                - !Sub arn:aws:dynamodb:${AWS::Region}:${AWS::AccountId}:table/${Table2}
                - !Sub arn:aws:dynamodb:${AWS::Region}:${AWS::AccountId}:table/${Table3}

inc_value_inside_map.py

# Not a beautiful code for the problem, but it handles 3 cases
# No map created
# Map created, but key doesn't exist
# Map created, key exists

# INPUT: size - the value to be added
# MAP Structure keys (dates / ), values (sizes accumulated)
# Used to count the amount of bytes consumed by day

dynamodb = boto3.resource('dynamodb', config=Config(max_pool_connections=30))
dynamodb_counter_table = dynamodb.Table(DDB_AUDIENCE_COUNTERS_TABLE)

day = datetime.datetime.today().strftime('%Y-%m-%d')

try:
  dynamodb_counter_table.update_item(
      Key={
          'CounterName': COUNTER_BYTES
      },
      UpdateExpression="SET #val.#age = #val.#day + :incr",
      ExpressionAttributeNames = {
          "#day": str(day),
          "#val": "Value"
      },
      ExpressionAttributeValues={
          ":incr": size,
      },
      ReturnValues="UPDATED_NEW"
  )
  except Exception: # Map created but key is not there
    print("WARN: update_bytes key not found. Trying to create key...")
    try:
        dynamodb_counter_table.update_item(
            Key={
                'CounterName': COUNTER_BYTES
            },
            UpdateExpression="SET #val.#day = :incr",
            ExpressionAttributeNames = {
                "#age": str(day),
                "#val": "Value"
            },
            ExpressionAttributeValues={
                ":incr": size,
            },
            ReturnValues="UPDATED_NEW"
        ) 
    except Exception: # No map created
        print("WARN: update_bytes map not found. Creating map...")
        dynamodb_counter_table.update_item(
            Key={
                'CounterName': COUNTER_BYTES
            },
            UpdateExpression="SET #val = :incr",
            ConditionExpression = "attribute_not_exists(#val)",
            ExpressionAttributeNames = {
                "#val": "Value"
            },
            ExpressionAttributeValues={
                ":incr": { str(day): size }
            }
        )