How to add python libraries to lambda using the CDK?

I want to use a library in my lambda function that was created by the CDK.

I did the following, without success:

1. add the library to my requirements.txt file

   Pillow

2. import the library in my lambda function

   from PIL import Image

3. install it and deploy

   source .env/bin/activate pip install -r requirements.txt cdk deploy`

Many thanks for any hints!