So I've recently ran into this issue, and I believe I found a cleaner way to import your layers.

First for the structure of the zip file which you upload:

• You do not need an __init__.py file
• Put all the scripts which you want to import into a folder name python
• Zip up that python folder (choose any name you want) and upload it to your layer
• Once uploaded, and the layer has been configured in your lambda function, you can simply use it with import {filename}

So if your script in the python folder was called something like custom_helper.py, import it in your lambda with import custom_helper.

I am not sure if this is the clean way to do it, but it seems simple enough to start.

I've seen that a few libraries like numpy and pandas don't work in Lambda when installed using pip. I have had success using the .whl package files for these libraries to create the Lambda layer. Refer to the steps below:

NOTE: These steps set up the libraries specific to the Python 3.7 runtime. If using any other version, you would need to download the .whl files corresponding to that Python version.

1. Create an EC2 instance using Amazon Linux AMI and SSH into this instance. We should create our layer in Amazon Linux AMI as the Lambda Python 3.7 runtime runs on this operating system (doc).

2. Make sure this instance has Python3 and "pip" tool installed.

3. Download the numpy .whl file for the cp37 Python version and the manylinux1_x86_64 OS by executing the below command:

$ wget https://files.pythonhosted.org/packages/d6/c6/58e517e8b1fb192725cfa23c01c2e60e4e6699314ee9684a1c5f5c9b27e1/numpy-1.18.5-cp37-cp37m-manylinux1_x86_64.whl

4. Skip to the next step if you're not using pandas. Download the pandas .whl file for the cp37 Python version and the manylinux1_x86_64 OS by executing the below command:

$ wget https://files.pythonhosted.org/packages/a4/5f/1b6e0efab4bfb738478919d40b0e3e1a06e3d9996da45eb62a77e9a090d9/pandas-1.0.4-cp37-cp37m-manylinux1_x86_64.whl

5. Next, we will create a directory named "python" and unzip these files into that directory:

        $ mkdir python
        $ unzip pandas-1.0.4-cp37-cp37m-manylinux1_x86_64.whl -d python/
        $ unzip numpy-1.18.5-cp37-cp37m-manylinux1_x86_64.whl -d python/

6. We also need to download "pytz" library to successfully import numpy and pandas libraries:

        $ pip3 install -t python/ pytz

7. Next, we would remove the “*.dist-info” files from our package directory to reduce the size of the resulting layer.

        $ cd python
        $ sudo rm -rf *.dist-info

8. This will install all the required libraries that we need to run pandas and numpy.

9. Zip the current "python" directory and upload it to your S3 bucket. Ensure that the libraries are present in the hierarchy as given here.

        $ cd ..
        $ zip -r lambda-layer.zip python/
        $ aws s3 cp lambda-layer.zip s3://YOURBUCKETNAME

10. The "lambda-layer.zip" file can then be used to create a new layer from the Lambda console.