InvalidLambdaResponseException for PreSignUp Trigger

Question

I keep getting the following error 
`InvalidLambdaResponseException: An error occurred (InvalidLambdaResponseException) when calling the SignUp operation: Unrecognizable lambda output`

whether I use boto3's `sign_up` or the JS `signUp` function. My trigger lambda is implemented in python and I autoconfirm and verify the user
```
event['response']['autoConfirmUser'] = True
event['response']['autoVerifyEmail'] = True
```

and return the event with `return event` .

The lambda works without any errors but I cannot figure out why I keep getting this error.

Accepted Answer

Found the error. We were using the `event["request"]` values for some internal logic in a separate function and that was modifying the values (forgot that dictionaries are passed by reference since they are mutable). Solved this by making a deep copy (using `copy.deepcopy(event["request"])`) before passing it on to the function.

Basically looks like the following

```python
from copy import deepcopy

def function_handler(event, context):
    # create a deep copy of the event request
    request = deepcopy(event['request'])
    # do something in our custom function, for us it returns a boolean
    response = do_something(request)
    if not response:
        # since our function did not work as expected, we cannot create the user, raising an exception
        raise Exception('do_something failed, here is an error message that makes sense...')
   
    # since do_something worked, let's confirm the user
    event['response']['autoConfirmUser'] = True
    event['response']['autoVerifyEmail'] = True
    
    return event
```

This worked. In retrospect, the error `Unrecognizable lambda output` is not really helpful, if it had more information on the `request` being modified it would have taken us much less time to figure this out.

InvalidLambdaResponseException for PreSignUp Trigger

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