Python library

A python library can be source code (to be interpreted) or precompiled. To call a library, it is used the import XXX keyword. The python utility will look in several location for several files.

• A file named XXX.py or XXX/__init__.py in the directory where python is run.
• A file named XXX.py or XXX/__init__.py in the PYTHONPATH environment variable, if it is set.
• A file named XXX.py or XXX/__init__.py in an installation-dependent list of directories configured at the time Python is installed

The last one is where external library are stored usually, to check where the file actually is use the sys python module:

python 
>>> import dolfinx
>>> dolfinx.__file__
'/home/mattia/miniconda3/envs/fenicsx-env/lib/python3.10/site-packages/dolfinx/__init__.py'