ModuleNotFoundError: No module named 'requests'

What it means

Python resolves imports by walking sys.path, and inside a Lambda execution environment that path is much shorter than the one you develop against. It contains /var/task, where your deployment package is extracted; /opt/python, where layers land; and the standard library that ships with the runtime. Your virtualenv is not there. Neither is anything pip installed globally on the build machine, nor anything reachable through a PYTHONPATH you set in a shell.

The import runs during init, while the runtime is loading your handler module, so the failure lands before your code executes and before there is an event to process. That is why you see no output of your own — not even a print at the top of the file — and why every invocation fails identically rather than intermittently.

Two structural details cause most real occurrences. The first is platform: any package with compiled components is distributed as platform-specific wheels, and a wheel installed on macOS or Apple Silicon is not loadable on an x86_64 Linux Lambda. Pip installs the wheel matching the machine it is running on unless told otherwise, so a build that works perfectly on a laptop produces an artifact that cannot import in production. The second is layer layout: a layer is extracted to /opt, but only /opt/python is on the import path, so a layer built without a top-level python/ directory attaches successfully, reports no error, and contributes nothing.

There is a third case worth separating out, because it looks the same and is not. When the message reads Unable to import module 'lambda_function', the module Lambda could not find is yours. The handler configuration is a dotted path of the form file.function with no .py extension, and if the file sits inside a directory in the zip, that directory belongs in the handler string too. Nothing is missing from the package in that case — Lambda is simply looking in the wrong place.

What it looks like in CloudWatch

This is the shape the failure arrives in: the lines of one invocation scattered among everything else the log group received at the same moment.

The panel on the right is generated by running the excerpt on the left through the same parser that powers the free web stitcher — it is what the tool actually produces for this input, not an illustration of it.

How to confirm it from the logs

The line appears before any of your own logging, immediately after INIT_START, because the import runs while the handler module is being loaded. The Python runtime writes it as [ERROR] Runtime.ImportModuleError: Unable to import module '<your_handler>': No module named '<package>', followed by a Traceback block. The handler module named in the first half is yours; the package named in the second half is the one that could not be found.

If the traceback shows the failure inside a package rather than in your own file, the missing module is a transitive dependency — something you installed depends on something that was not installed with it.

Causes, most likely first

Fixes

bashpip install \
  --target ./package \
  --platform manylinux2014_x86_64 \
  --implementation cp \
  --python-version 3.12 \
  --only-binary=:all: \
  -r requirements.txt

cd package && zip -qr ../function.zip . && cd ..
zip -q function.zip lambda_function.py

bash# Correct layer layout:
#   python/requests/...
#   python/urllib3/...
mkdir -p python
pip install -r requirements.txt --target python/
zip -qr layer.zip python/

bashdocker run --rm --platform linux/amd64 \
  -v "$PWD":/var/task \
  public.ecr.aws/lambda/python:3.12 \
  pip install -r requirements.txt --target /var/task/package

Also seen as

The same underlying failure, worded differently by a different runtime, SDK version, or logging layer. All of these land here — there is no separate page for each phrasing.

Related errors

Errors that show up alongside this one, or that people mistake for it.

References

• AWS Lambda Developer Guide — Working with .zip file archives for Python
• AWS Lambda Developer Guide — Working with layers