Data loader plugins sometimes need custom Python packages. These can be provided in the pkg folder, relative to where the data loader is invoked.
The recommendation is to include a requirements.txt file in the folder where the data loader plugin is located. That file lists all the required packages, with one package dependency per line. For example:
dateutils

To download these packages into the pkg folder, execute the following command (the pkg folder must exist before calling this command):
pip install -r requirements.txt --root pkg