Details on the AWS Lambda Python LambdaContext context object when instantiated from a CloudFormation stack

example_aws_lambda_cloudformation_context.md

LambdaContext

Here is the raw output from examining the Python LambdaContext context object in a AWS Lambda function when called from a CloudFormation stack. More information on the context object can be found here : http://docs.aws.amazon.com/lambda/latest/dg/python-context-object.html

LambdaContext object : print(context)

<__main__.LambdaContext object at 0x7fd706780710>

LambdaContext vars : vars(context)

{
    'aws_request_id': 'a3de505e-f16b-42f4-b3e6-bcd2e4a73903',
    'log_stream_name': '2015/10/26/[$LATEST]c71058d852474b9895a0f221f73402ad',
    'invoked_function_arn': 'arn:aws:lambda:us-west-2:123456789012:function:ExampleCloudFormationStackName-ExampleLambdaFunctionResourceName-AULC3LB8Q02F',
    'client_context': None,
    'log_group_name': '/aws/lambda/ExampleCloudFormationStackName-ExampleLambdaFunctionResourceName-AULC3LB8Q02F',
    'function_name': 'ExampleCloudFormationStackName-ExampleLambdaFunctionResourceName-AULC3LB8Q02F',
    'function_version': '$LATEST',
    'identity': <__main__.CognitoIdentity object at 0x7fd7042a2b90>,
    'memory_limit_in_mb': '128'
} 

LambdaContext dir : dir(context)

[
    '__class__',
    '__delattr__',
    '__dict__',
    '__doc__',
    '__format__',
    '__getattribute__',
    '__hash__',
    '__init__',
    '__module__',
    '__new__',
    '__reduce__',
    '__reduce_ex__',
    '__repr__',
    '__setattr__',
    '__sizeof__',
    '__str__',
    '__subclasshook__',
    '__weakref__',
    'aws_request_id',
    'client_context',
    'function_name',
    'function_version',
    'get_remaining_time_in_millis',
    'identity',
    'invoked_function_arn',
    'log',
    'log_group_name',
    'log_stream_name',
    'memory_limit_in_mb'
]

context.succeed()

The Python runtime does not have the equivalent of a context.succeed(), context.done() or context.fail().

In order to achieve the same thing, merely return from the handler function to succeed or raise an exception to fail

def lambda_handler(event, context):
    if event['variable_name'] == 1:
        return { 
            'message' : 'We are done'
        }
    else:
        raise Exception('Sending failure')

What does it look like from AWS's side

@NovemberOscar points out this code which shows what AWS sees on their side for the Python context

https://github.com/aws/aws-lambda-python-runtime-interface-client/blob/main/awslambdaric/lambda_context.py

Just found this, but for anyone else looking, AWS Lambda's Python runtime does not have a succeed() capability. I'm not sure why of the disparity between the two runtimes, but a successful return (whether controlled exceptions via a catch block or normal execution) is what tells Lambda to succeed the invocation.

And more details here :) (it's official!)

https://github.com/aws/aws-lambda-python-runtime-interface-client/blob/main/awslambdaric/lambda_context.py

Where do I put the response body? How can I mapping template response headers out of it? All I can do is set errorMessage with an exception, right? 304 Not Modified, where does ETag go?