AWS StepFunction : Getting Error as "error": "KeyError"

Question

I am new to AWS and Step functions. I am trying to run simple program from Step function using Lambda function. I have tried below code to run the Step function.

code:

import boto3
import json
import os



def lambda_handler(event, context):


    subject = event['Mail']['subject']
    toList = event['Mail']['mailTo'] 
    message = event['MailMessage']['message']
    status = ""


    body = message 

    subject="["+status+"]"+subject


    for to in toList.split(","):
        sendMail(to, ADMIN_EMAIL, subject, body)

    return event


def sendMail(to, reply, subject, body):
    client = boto3.client('ses', region_name=region_name)
    response = client.send_email(
        Source=reply,
        Destination={
            'ToAddresses': [
                to,
            ]
        },
        Message={
            'Subject': {
                'Data': subject,
            },
            'Body': {
                'Text': {
                    'Data': body,
                },
            }
        },
        ReplyToAddresses=[
            reply,
        ],
        ReturnPath=reply
    )
    return response

after running the Step function, I am getting below error.

{
  "error": "KeyError",
  "cause": {
    "errorMessage": "'Mail'",
    "errorType": "KeyError",
    "stackTrace": [
      [
        "/var/task/lambda_function.py",
        11,
        "lambda_handler",
        "subject = event['Mail']['subject']"
      ]
    ]
  }
}

My step function :

{
  "Comment": "A Sample program to send an email",
  "StartAt": "SampleMail",
  "States": {
    "SampleMail": {
      "Type": "Task",
     "Resource": "arn:aws:lambda:us-west-1:000000123:function:TestEmail", 

      "End": true
    }
  }
}

could you please tell me what i am missing here?

Kindly help me.

Many thanks for your help.

Find out what is in the event dict: coderwall.com/p/gmxnqg/pretty-printing-a-python-dictionary — jarmod
– jarmod, Commented Oct 30, 2018 at 3:10

Daryl T · Accepted Answer · 2018-10-30 02:43:32Z

2

The event passed to your lambda_handler function does not have a key called "Mail", so this line

subject = event['Mail']['subject']

is failing. You should verify the event parameter has a 'Mail' attribute before retrieving any values with that key.

answered Oct 30, 2018 at 2:43

Daryl T

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5 Comments

lakshmiprathyusha Over a year ago

Hi, Thanks for the response. Where to check whether this key is exists? how to add parameter?

lakshmiprathyusha Over a year ago

Do i need to create a API GATEWAY Parameter for this Step function?Like body, query, or path parameters in aws

Daryl T Over a year ago

You can open an execution of your Step Function and click the step where it calls your Lambda function. You should see an Input option to see what gets passed to your Lambda function.

lakshmiprathyusha Over a year ago

Hi, I am passing Mail (subject,To,Mesage).But still it is failing.

Daryl T Over a year ago

Your code is expecting event to be of the form { "Mail" : { "subject": "", "mailTo": ""}, "MailMessage": { "message" : "" } }. Confirm that data is passed to the Lambda function in that form.

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