Return python string as the body of HTTP response

Question

I am using AWS Lambda with python-2.7 replying back to AWS Api Gateway . My lambda function should return a response looking like following, but I am strugling with putting the proper form of body in the JSON response:

    return_value = {
        "statusCode": 200,
        "isBase64Encoded": 'false',
        "headers": {"Content-Type": "application/json"},
        "body": {payload['note']}
    }

the type of payload['note'] is unicode , so I don't know what exactly to put in the brackets opposite to body , as I am new to python and tried a lot without being able to figure it out. I tried to convert it to string using:

unicodedata.normalize('NFKD', payload['note']).encode('ascii', 'ignore')

But it didn't work either.

Answer 1

First, I believe it is a good idea to convert the unicode string to a python string before, since I dont know if the rest of your code can handles unicode in json.

I think your problem is related to json formatting. As JSON, the body field should contain key-value pairs.

Try with :

return_value = {
    "statusCode": 200,
    "isBase64Encoded": 'false',
    "headers": {"Content-Type": "application/json"},
    "body": {"note": payload['note']}
}

Answer 2

It's probably best to build it using standard objects first, then convert it to JSON as you return it. For example:

# coding=utf-8

import json

def aws_message(payload):
  message = dict(statusCode=200,
                 isBase64Encoded=False,
                 headers={"Content-Type": "application/json"},
                 body=payload['note'])
  return json.dumps(message)


if __name__=="__main__":
    payload = dict(note='something')
    print(aws_message(payload))

Unfortunately you'll notice I switched from the long-form dict() creation to the short-hand when building the headers inside the message (it was a quick 'n dirty example). Here is the output:

C:\Python37\python.exe C:/dev/scratches/scratch_17.py
{"statusCode": 200, "isBase64Encoded": false, "headers": {"Content-Type": "application/json"}, "body": "something"}

As you can see, it's quite straight-forward to build the object in a fashion that is easy to understand, and then let the json library do all the conversion into a correctly-formatted response. I hope this helps.