'serverless invoke -f hello' gives KeyError - serverless-framework

Question

I am following a tutorial in order to learn how to work with the serverless framework. The goal is to deploy a Django application. This tutorial suggests putting the necessary environment variables in a separate yml-file. Unfortunately, following the tutorial gets me a KeyError.
I have a serverless.yml, variables.yml and a handler.py. I will incert all code underneath, together with the given error.
serverless.yml:
service: serverless-django
custom: ${file(./variables.yml)}
provider:
name: aws
runtime: python3.8
functions:
hello:
environment:
- THE_ANSWER: ${self:custom.THE_ANSWER}
handler: handler.hello
variables.yml:
THE_ANSWER: 42
handler.py:
import os
def hello(event, context):
return {
"statusCode": 200,
"body": "The answer is: " + os.environ["THE_ANSWER"]
}
The error in my terminal:
{
"errorMessage": "'THE_ANSWER'",
"errorType": "KeyError",
"stackTrace": [
" File \"/var/task/handler.py\", line 7, in hello\n \"body\": \"The answer is: \" + os.environ[\"THE_ANSWER\"]\n",
" File \"/var/lang/lib/python3.8/os.py\", line 675, in __getitem__\n raise KeyError(key) from None\n"
]
}
Error --------------------------------------------------
Error: Invoked function failed
at AwsInvoke.log (/snapshot/serverless/lib/plugins/aws/invoke/index.js:105:31)
at AwsInvoke.tryCatcher (/snapshot/serverless/node_modules/bluebird/js/release/util.js:16:23)
at Promise._settlePromiseFromHandler (/snapshot/serverless/node_modules/bluebird/js/release/promise.js:547:31)
at Promise._settlePromise (/snapshot/serverless/node_modules/bluebird/js/release/promise.js:604:18)
at Promise._settlePromise0 (/snapshot/serverless/node_modules/bluebird/js/release/promise.js:649:10)
at Promise._settlePromises (/snapshot/serverless/node_modules/bluebird/js/release/promise.js:729:18)
at _drainQueueStep (/snapshot/serverless/node_modules/bluebird/js/release/async.js:93:12)
at _drainQueue (/snapshot/serverless/node_modules/bluebird/js/release/async.js:86:9)
at Async._drainQueues (/snapshot/serverless/node_modules/bluebird/js/release/async.js:102:5)
at Immediate._onImmediate (/snapshot/serverless/node_modules/bluebird/js/release/async.js:15:14)
at processImmediate (internal/timers.js:456:21)
at process.topLevelDomainCallback (domain.js:137:15)
For debugging logs, run again after setting the "SLS_DEBUG=*" environment variable.
Get Support --------------------------------------------
Docs: docs.serverless.com
Bugs: github.com/serverless/serverless/issues
Issues: forum.serverless.com
Your Environment Information ---------------------------
Operating System: linux
Node Version: 12.18.1
Framework Version: 2.0.0 (standalone)
Plugin Version: 4.0.2
SDK Version: 2.3.1
Components Version: 3.1.2
The command i'm trying is 'sls invoke -f hello'. The command 'sls deploy' has been already executed succesfully.
I am new to serverless, so please let me know how to fix this, or if any more information is needed.

Answer 1

First of all, there is an error in yml script:
Serverless Error ---------------------------------------
Invalid characters in environment variable 0
The error is defining environment variables as an array instead of key-value pairs
And then after deployment, everything works smoothly (sls deploy -v)
sls invoke --f hello
{
"statusCode": 200,
"body": "The answer is: 42"
}
serverless.yml
service: sls-example
custom: ${file(./variables.yml)}
provider:
name: aws
runtime: python3.8
functions:
hello:
environment:
THE_ANSWER: ${self:custom.THE_ANSWER}
handler: handler.hello
variables.yml
THE_ANSWER: 42