Feature request: Return empty Dict or List in Event Source Data Classes instead of None

Use case

Arguably, it might be easier for users if an empty Dict is returned instead of None for path_parameters in APIGatewayProxyEventV2, for example.

Instead of:

@event_source(data_class=APIGatewayProxyEventV2)
def lambda_handler(event: APIGatewayProxyEventV2, context) -> None:
    parameters = event.path_parameters or {}
    handle(parameters["id"])

it would become:

@event_source(data_class=APIGatewayProxyEventV2)
def lambda_handler(event: APIGatewayProxyEventV2, context) -> None:
    handle(event.path_parameters["id"])

Ultimately this approach could be followed for any return value that is either an Optional[Dict] or an Optional[List], returning an empty Dict or List instead of None in all cases:

utilities/data_classes/api_gateway_proxy_event.py
- APIGatewayEventAuthorizer
  - def claims(self) -> Dict[str, Any]
  - def scopes(self) -> List[str]
- APIGatewayProxyEvent
  - def multi_value_query_string_parameters(self) -> Dict[str, List[str]]
  - def path_parameters(self) -> Dict[str, str]
  - def stage_variables(self) -> Dict[str, str]
- RequestContextV2AuthorizerIam
  - def cognito_amr(self) -> List[str]
- RequestContextV2Authorizer
  - def jwt_claim(self) -> Dict[str, Any]
  - def jwt_scopes(self) -> List[str]
  - def get_lambda(self) -> Dict[str, Any]
- APIGatewayProxyEventV2
  - def cookies(self) -> List[str]
  - def path_parameters(self) -> Dict[str, str]
  - def stage_variables(self) -> Dict[str, str]

and so on...

The bottom line is: Does it matter for users to differentiate between None and an empty Dict or List for any Event Source Data Classe property? If it does for a particular one, it an exception to a rule or the rule?

This change would be backwards compatible with the previous code.

This approach was already implemented in only one place so far, as far as I could check:

utilities/data_classes/common.py
- BaseProxyEvent
  - def headers(self) -> Dict[str, str]

Solution/User Experience

Solution can be the same as for the headers in the BaseProxyEvent:

powertools-lambda-python/aws_lambda_powertools/utilities/data_classes/common.py

Lines 98 to 100 in 1905e4c

    
           @property 
        
           def headers(self) -> Dict[str, str]: 
        
               return self.get("headers") or {}

Alternative solutions

No response

Acknowledgment

This feature request meets Powertools for AWS Lambda (Python) Tenets
Should this be considered in other Powertools for AWS Lambda languages? i.e. Java, TypeScript, and .NET

@ericbn

Hi @ericbn thank you for sending this proposal! Two notes:

Do you agree that code that backwards compatibility can be ensured since existing code that relies on None as a valid value will still function correctly?
Providing specific use cases and examples where this feature significantly improves the developer experience would strengthen the proposal.

It seems to be this would be a big breaking change anyways. So we might have to open an RFC to discuss this with the larger community and consider the breaking change for v3.

Hi. Totally agree this is a breaking change for existing code that relies on None as a valid value. Good point. I see the change in the headers method in BaseProxyEvent was done exactly to keep backward compatibility.

I propose this change is favor of an API with multiple methods like get_query_string_value and get_header_value in BaseProxyEvent.

powertools-lambda-python/aws_lambda_powertools/utilities/data_classes/common.py

Lines 139 to 157 in 2c44207

    
               def get_query_string_value(self, name: str, default_value: Optional[str] = None) -> Optional[str]: 
        
                   """Get query string value by name 
        
                   Parameters 
        
                   ---------- 
        
                   name: str 
        
                       Query string parameter name 
        
                   default_value: str, optional 
        
                       Default value if no value was found by name 
        
                   Returns 
        
                   ------- 
        
                   str, optional 
        
                       Query string parameter value 
        
                   """ 
        
                   return get_query_string_value( 
        
                       query_string_parameters=self.query_string_parameters, 
        
                       name=name, 
        
                       default_value=default_value, 
        
                   )

powertools-lambda-python/aws_lambda_powertools/utilities/data_classes/common.py

Lines 159 to 186 in 2c44207

    
               # Maintenance: missing @overload to ensure return type is a str when default_value is set 
        
               def get_header_value( 
        
                   self, 
        
                   name: str, 
        
                   default_value: Optional[str] = None, 
        
                   case_sensitive: Optional[bool] = False, 
        
               ) -> Optional[str]: 
        
                   """Get header value by name 
        
                   Parameters 
        
                   ---------- 
        
                   name: str 
        
                       Header name 
        
                   default_value: str, optional 
        
                       Default value if no value was found by name 
        
                   case_sensitive: bool 
        
                       Whether to use a case-sensitive look up 
        
                   Returns 
        
                   ------- 
        
                   str, optional 
        
                       Header value 
        
                   """ 
        
                   return get_header_value( 
        
                       headers=self.headers, 
        
                       name=name, 
        
                       default_value=default_value, 
        
                       case_sensitive=case_sensitive, 
        
                   )

Pros:

No need to create extra methods in the data classes.
User can use the List and Dict API directly, for example to choose between event.query_string_parameters["foo"] or event.query_string_parameters.get("foo") or event.query_string_parameters.get("foo", "default_foo") in case the key is required or not, or to use other functions like first(event.cookies).

Cons(?):

As the List and Dict APIs are used directly, a parameter like case_sensitive in get_header_value would have to be replaced by returning a custom CaseInsensitiveDict.

@ericbn

Hello @ericbn! We've updated our roadmap and included this feature request. We are planning to release this feature in Powertools v3.

Roadmap for v3: https://docs.powertools.aws.dev/lambda/python/latest/roadmap/#v3

Sure, I’ll wait. Makes perfect sense. Looking forward for my first contribution with a PR to the project!

Took a long time (stability/backwards compatibility) but we've started implementing for v3: #4189

@heitorlessa

Oi @heitorlessa. I'll be happy to work on this as a contribution to the project.

Closed via #4606

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Feature request: Return empty Dict or List in Event Source Data Classes instead of None #2605

Use case

Solution/User Experience

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Acknowledgment

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	@property
	def headers(self) -> Dict[str, str]:
	return self.get("headers") or {}

	def get_query_string_value(self, name: str, default_value: Optional[str] = None) -> Optional[str]:
	"""Get query string value by name

	Parameters
	----------
	name: str
	Query string parameter name
	default_value: str, optional
	Default value if no value was found by name
	Returns
	-------
	str, optional
	Query string parameter value
	"""
	return get_query_string_value(
	query_string_parameters=self.query_string_parameters,
	name=name,
	default_value=default_value,
	)

	# Maintenance: missing @overload to ensure return type is a str when default_value is set
	def get_header_value(
	self,
	name: str,
	default_value: Optional[str] = None,
	case_sensitive: Optional[bool] = False,
	) -> Optional[str]:
	"""Get header value by name

	Parameters
	----------
	name: str
	Header name
	default_value: str, optional
	Default value if no value was found by name
	case_sensitive: bool
	Whether to use a case-sensitive look up
	Returns
	-------
	str, optional
	Header value
	"""
	return get_header_value(
	headers=self.headers,
	name=name,
	default_value=default_value,
	case_sensitive=case_sensitive,
	)

Feature request: Return empty Dict or List in Event Source Data Classes instead of None #2605

Description

Use case

Solution/User Experience

Alternative solutions

Acknowledgment

Activity

rubenfonseca commented on Jun 29, 2023

ericbn commented on Jul 11, 2023

leandrodamascena commented on Aug 17, 2023

3 remaining items

ericbn commented on Aug 23, 2023

heitorlessa commented on Jun 10, 2024

ericbn commented on Jun 10, 2024

leandrodamascena commented on Jul 29, 2024

github-actions commented on Jul 29, 2024

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