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Python relative imports in AWS Lambda fail with `attempted relative import with no known parent package`

Python relative imports in AWS Lambda fail with attempted relative import with no known parent package

The Problem

In AWS Lambda if I attempt an explicit relative import like this

.
├── lambda_file.py
└── example.py
# lambda_file.py
from .example import lambda_handler
# example.py
def lambda_handler(event, context):
    return True

And I configure AWS Lambda's handler to lambda_file.lambda_handler I get the following errors

  • Python 2.7 : Attempted relative import in non-package
  • Python 3.7 : attempted relative import with no known parent package

Why use explicit relative imports

PEP008 says :

Implicit relative imports should never be used and have been removed in Python 3.

How to workaround by using implicit relative imports

If I change lambda_file.py to contain the following, it works, but no longer uses explicit relative imports

# lambda_file.py
from example import lambda_handler

How to correctly solve the problem

The solution is to ensure that the "Handler" value that you configure in AWS Lambda contain at least 2 . periods. To achieve this you need to put your code within a directory in your AWS Lambda code zip file and make that directory a module by adding an empty __init__.py file. The resulting structure looks like this

.
├── app
│   ├── __init__.py
│   ├── lambda_file.py
│   └── example.py

And you now change the "Handler" value from lambda_file.lambda_handler to app.lambda_file.lambda_handler

Additional Notes

@hawkins

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hawkins commented Feb 26, 2020

Thanks for this info - I was just running into this for the N-th time today and couldn't recall the solution!

AWS Lambda loads your handler as a module import not as a top-level script

Do you have a link to the docs for this or is it something you just figured out? Maybe just by reading the lambda Python runtime source code?

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