Module aws_lambda_powertools.utilities.parser.parser

Functions

def event_parser(handler: Callable[..., EventParserReturnType], event: dict[str, Any], context: LambdaContext, model: type[T] | None = None, envelope: type[Envelope] | None = None, **kwargs: Any)

Lambda handler decorator to parse & validate events using Pydantic models

It requires a model that implements Pydantic BaseModel to parse & validate the event.

When an envelope is given, it'll use the following logic:

1. Parse the event against the envelope model first e.g. EnvelopeModel(**event)
2. Envelope will extract a given key to be parsed against the model e.g. event.detail

This is useful when you need to confirm event wrapper structure, and b) selectively extract a portion of your payload for parsing & validation.

NOTE: If envelope is omitted, the complete event is parsed to match the model parameter definition.

Example

Lambda handler decorator to parse & validate event

class Order(BaseModel):
    id: int
    description: str
    ...

@event_parser(model=Order)
def handler(event: Order, context: LambdaContext):
    ...

Lambda handler decorator to parse & validate event - using built-in envelope

class Order(BaseModel):
    id: int
    description: str
    ...

@event_parser(model=Order, envelope=envelopes.EVENTBRIDGE)
def handler(event: Order, context: LambdaContext):
    ...

Parameters

handler :  Callable

Method to annotate on

event :  dict

Lambda event to be parsed & validated

context :  LambdaContext

Lambda context object

model : type[T] | None

Your data model that will replace the event.

envelope : Envelope

Optional envelope to extract the model from

Raises

ValidationError

When input event does not conform with model provided

InvalidModelTypeError

When model given does not implement BaseModel or is not provided

InvalidEnvelopeError

When envelope given does not implement BaseEnvelope

def parse(event: dict[str, Any], model: type[T], envelope: type[Envelope] | None = None)

Standalone function to parse & validate events using Pydantic models

Typically used when you need fine-grained control over error handling compared to event_parser decorator.

Example

Lambda handler decorator to parse & validate event

from aws_lambda_powertools.utilities.parser import ValidationError

class Order(BaseModel):
    id: int
    description: str
    ...

def handler(event: Order, context: LambdaContext):
    try:
        parse(model=Order)
    except ValidationError:
        ...

Lambda handler decorator to parse & validate event - using built-in envelope

class Order(BaseModel):
    id: int
    description: str
    ...

def handler(event: Order, context: LambdaContext):
    try:
        parse(model=Order, envelope=envelopes.EVENTBRIDGE)
    except ValidationError:
        ...

Parameters

event :  dict

Lambda event to be parsed & validated

model :  Model

Your data model that will replace the event

envelope : Envelope

Optional envelope to extract the model from

Raises

ValidationError

When input event does not conform with model provided

InvalidModelTypeError

When model given does not implement BaseModel

InvalidEnvelopeError

When envelope given does not implement BaseEnvelope