Accessing query parameter in Lambda with Python

Question

Hi All,

I am trying to build Lambda function with python. I am trying to access header, request ,query parameter passed as a part of request . I am able to access body part using <Event> like <event['Number1']> but not able to access other request or header parameter . Have tried like <event['pathParameters']['token']> but of no use.

Can anyone please help on this.

Thanks

Baharul Islam

Comments

@Baharul can you help me with some more detail as what are you actually trying to do? What kind of request are you processing and what are the different fields?

---

Hi ,

I am trying to develop some AWS rest API using python.In API I want to retrieve all transport info like content_type, http method , client Ip address. 
Also in get and put method want to get header information like userID, userGroup and request header as maybe Policy-No as per below image.

Thanks

Baharul Islam

---

@Baharul, great I came to know as what you are trying to achieve. 

You can  use this to get your query string

{
    "querystring": "$input.params().querystring"
}

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Thanks @Shuvodip.

I was looking for code in Python. Also for aws Lambda I think we need to get it using <event or context>

---

@Baharul, yes you can use 

event["queryStringParameters"]['queryparam1']

to access the query, did you use this? In your question you said it didn't work. What error did you get?

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@Baharul have you checked the Lambda Proxy Integration?

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Hi Shuvodip,

I am getting error as without Lambda proxy integration

{
   "errorMessage": "'queryStringParameters'",
   "errorType": "KeyError",
   "stackTrace": ["  File \"/var/task/lambda_function.py\", line 23, in lambda_handler\n    \"querystring\": event[\"queryStringParameters\"]['userID']\n"]
}

As soon as I am enabling proxy integration I am getting bad request gateway  request. Only difference between this two is proxy integration.

HTTP/1.1 502 Bad Gateway
Date: Wed, 05 Dec 2018 13:38:36 GMT
Content-Type: application/json
Content-Length: 36
Connection: keep-alive
x-amzn-RequestId: 10d81e71-f893-11e8-92fb-b9ef3d2c5a0f
x-amz-apigw-id: Rb4yZG5CCYcFnvQ=

{"message": "Internal server error"}

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@Baharul check the format of the response of your lambda function. Generally this error occurs when there is a permission issue or the response of lambda function is not as per the required format.

---

Hi @Shuvodip ,

I have made simple lambda code as below with Integration Proxy as enabled.

import json

def lambda_handler(event, context):
    # TODO implement
    number1 = event['Number1']
    number2 = event['Number2']
    sum = number1 + number2
    #querystring= event["queryStringParameters"]['test']
    querystring=context["test"]
    Body = {
        "response":{
           "resultStatus": "SUCCESS",
           "results":{
               "Number1": number1,
               "Number2": number2,
               "Sum": sum,
               "querystring": querystring
           }
        }
    }
    return {
        'statusCode': 200,
        'body': Body
    }
    

But when running the API I am getting error as

{
   "errorMessage": "'LambdaContext' object is not subscriptable",
   "errorType": "TypeError",
   "stackTrace": ["  File \"/var/task/lambda_function.py\", line 9, in lambda_handler\n    querystring=context[\"test\"]\n"]
}

Can anyone please help on this point.

Thanks

Baharul Islam

---

Hey @Baharul, Sorry for the long delay but I am unable to understand the problem you are facing here.

---

@Baharul I got a documentation of a similar thing that you are trying to do here:

https://docs.aws.amazon.com/apigateway/latest/developerguide/integrating-api-with-aws-services-lambda.html

---

import json

def lambda_handler(event, context):
    # TODO implement
    number1 = event['Number1']
    number2 = event['Number2']
    sum = number1 + number2
    #querystring= event["queryStringParameters"]['test']
    querystring=context["test"]  #what are you trying to achieve here?
    Body = {
        "response":{
           "resultStatus": "SUCCESS",
           "results":{
               "Number1": number1,
               "Number2": number2,
               "Sum": sum,
               "querystring": querystring
           }
        }
    }
    return {
        'statusCode': 200,
        'body': Body
    }

---

Thanks Shuvodip.

Here I am just trying to retrieve parameter that are pass as a part of query parameter in url like ?EmployeeID=456

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Hey @baharul 

See this lambda function

def lambda_handler(event, context):
   num1 = event["queryStringParameters"]["num1"]
    num2 = event["queryStringParameters"]["num2"]
    sum =int(num1) + int(num2)
    response = {}
    response["headers"] = event["headers"]
    response["sum"] = sum
    response["num1"] = num1
    response["num2"] = num2
    return {
        'statusCode': 200,
        'body': json.dumps(event)
    }

You get everything under event itself. Try using it and let me know.

---

Thanks Shuvodip. When I am trying to run the same from SoapUI via API gateway getting error as 

{
   "errorMessage": "'headers'",
   "errorType": "KeyError",
   "stackTrace": ["  File \"/var/task/lambda_function.py\", line 10, in lambda_handler\n    response[\"headers\"] = event[\"headers\"]\n"]
}

Please refer below screen for more details...

Lambda Function

Gateway

Soup UI test

Answer 1

Have you gone through the mapping template reference provided by Amazon
https://docs.aws.amazon.com/apigateway/latest/developerguide/api-gateway-mapping-template-reference.html

You can see how they are accessing the query string.

For more info on AWS Lambda, refer to https://www.youtube.com/watch?v=XjPUyGKRjZs

Hope this helps!!

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Thanks!