capo-lambda: typed, async Python SDK for AWS Lambda¶

capo-lambda is a typed Python SDK for AWS Lambda. It has an async client, AsyncLambdaClient, for asyncio and trio, and a sync client, LambdaClient, with the same methods. Requests and responses are typed with TypedDicts, so your editor and type checker know every field.

It is part of capo, a community-driven alternative to boto3 and aioboto3, built on its own HTTP stack instead of botocore and generated from the official AWS Smithy models. Documentation: https://capo-sdk.dev/services/lambda/

Installation¶

pip install capo-lambda

Usage¶

from capo_lambda import AsyncLambdaClient


async def main():
    async with AsyncLambdaClient() as lambda_:
        # Example: call the delete_function operation
        response = await lambda_.delete_function()
        print(response["status_code"])

Pagination¶

Some operations in this SDK support pagination. If the operation supports pagination it will have an iter_ prefixed method that returns an async iterator.

from capo_lambda import AsyncLambdaClient


async def main():
    async with AsyncLambdaClient() as lambda_:
        # Example: paginate over list_capacity_providers
        async for item in lambda_.iter_list_capacity_providers():
            print(item)

Streaming Request¶

Some operations accept a streaming request body. Pass an async iterator of bytes chunks, or the whole body as bytes, for the streaming parameter.

A plain iterator can be sent only once, so if a request fails after its body was transmitted the operation is not retried. To get retries for streamed uploads, pass a Body instead: it wraps a source that can be reopened, and every attempt streams a fresh copy. Body.from_path (sync client) and Body.async_from_path (async client, needs anyio) stream a file from disk; Body(opener) takes any context manager that yields a (stream, length) pair.

from capo_lambda import AsyncLambdaClient, Body


async def main():
    async with AsyncLambdaClient() as lambda_:
        # Example: call invoke_async with a streaming request body
        async def chunks():
            yield b'Hello, World!'

        response = await lambda_.invoke_async(invoke_args=chunks())
        print(response)

        # Or pass the whole body as bytes
        response = await lambda_.invoke_async(invoke_args=b'Hello, World!')
        print(response)

        # Or stream a file with Body: the file is reopened on every retry
        # and Content-Length is taken from its size, so no content_length needed
        response = await lambda_.invoke_async(invoke_args=Body.async_from_path("hello.txt"))
        print(response)

Waiters¶

Waiters poll an operation until a resource reaches a desired state. If the operation supports waiters it will have a wait_until_ prefixed method.

from capo_lambda import AsyncLambdaClient


async def main():
    async with AsyncLambdaClient() as lambda_:
        # Example: wait for function_exists
        await lambda_.wait_until_function_exists(max_wait_time=300)

Error Handling¶

The SDK raises exceptions for errors returned by the API. Catch them to handle failures gracefully.

from capo_lambda import AsyncLambdaClient
from capo_lambda.error import InvalidParameterValueException


async def main():
    async with AsyncLambdaClient() as lambda_:
        try:
            await lambda_.delete_function()
        except InvalidParameterValueException as e:
            print(f"Error: {e}")
            print(e.data)  # additional error data

Retrying¶

The SDK retries failed operations automatically. Retry behaviour follows the Smithy specification: errors are retried based on their is_retryable and is_throttling_error attributes. Throttling errors use a longer base delay. Network-level failures (connection errors and timeouts) are also retried. Non-retryable errors, such as client errors without the @retryable trait, are raised immediately without further attempts.

The number of attempts defaults to 3 and can be changed at the client level via retry_max_attempts, or per call via config_overrides.

from capo_lambda import AsyncLambdaClient


async def main():
    async with AsyncLambdaClient() as lambda_:
        # Default: 3 attempts for every operation
        response = await lambda_.delete_function()

        # Override per operation
        response = await lambda_.delete_function(config_overrides={"retry_max_attempts": 5})

        # Disable retries for this call
        response = await lambda_.delete_function(config_overrides={"retry_max_attempts": 1})