Class based AWS lambda in Python

Question

I have created a class based AWS lambda function in python called requestHandler.py as below

from action_dispatcher import ActionDispatcher

class RequestHandler(ActionDispatcher):


    @staticmethod
    def createTemplate(event, context):
        return "Hello world"

My action_dispatcher.py is as shown below.

import json

class ActionDispatcher(object):

    def __call__(self, event, context, *args, **kwargs):

        action = event.get('action')
        handler = getattr(self, action, None)

        if handler is None:
            return json.loads({'status': 'error', 'code': 404, 'message':"Action {0} not found.".format(action) })

        return handler(request, *args, **kwargs)

With this above setup and lambda handler as requestHandler.RequestHandler, i get error "RequestHandler() takes no arguments" in this case i create action as createTemplate. so i want to call this method from RequestHandler.

Jacinator · Accepted Answer · 2019-04-02 12:41:10Z

2

It looks to me like you are trying to call your class instead of an instance of the class. RequestHandler() will call the __init__ method to initialize an instance of the class. Since you haven't defined the method it doesn't take any arguments. To access __call__ you need to call an instance of your class.

handler = RequestHandler()
result = handler(request, context, *args, **kwargs)

answered Apr 2, 2019 at 12:41

Jacinator

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2 Comments

santosh Over a year ago

This is with respect to AWS lambda invoking, so need suggestion based on that

Jacinator Over a year ago

I'm afraid I don't know much (or anything) about AWS. Your error message looks like you are trying to instantiate the RequestHandler with arguments instead of call an instance, which Python won't allow with your current code. Could you post the line of code where the call is happening?

Deiv · Accepted Answer · 2019-04-02 21:17:02Z

1

You can only define a handler in python using def handler(event, context):. However, I found a package that allows you to call the handler as a class

Usage, as noted in their documentation, is as follows:

pip install aws-lambda-handler

import aws_lambda

class EchoHandler(aws_lambda.Handler):
    """Echo handler."""

    def perform(self, request, **k):
        """Echo perform method."""
        response = aws_lambda.Response()
        response.body = self.request.event
        return response

echo_handler = EchoHandler()

# `echo_handler` is now a callable function you can map your AWS Lambda function to

answered Apr 2, 2019 at 21:17

Deiv

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Comments

santosh · Accepted Answer · 2019-04-03 09:31:54Z

0

The solution for my problem was simple, as mentioned by jacinator, i should try with class instance. earlier for lambda handler, i used pass class as handler, now i am passing the instance of the class as handler. Added the line in requestHandler.py rhandler = RequestHandler() So previously my lambda handler was like requestHandler.RequestHandler, now it has been changed to requestHandler.rhandler.

answered Apr 3, 2019 at 9:31

santosh

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