Asking user for paths to other software in Python scripts: best practices?

Question

I'm developing a Python package for automating an existing piece of software. This software (FreeCAD) comes with a bunch of Python modules and is installed separately by the user.

My package has to know where FreeCAD is installed before it is imported:

mymodule.py

if user_has_not_told_me_where_freecad_is:
  sys.path.append('/path/to/default/freecad/bin')
else:
  use_user_supplied_path

import FreeCAD

I want my users to be able to do in, say, a Jupyter Notebook, or a standalone script:

user_script.ipynb

# this is where the user will tell me where freecad is
set_freecad_path('/path/to/freecad/bin')

import mymodule
# ... do other stuff

Things I tried

I don't think I can do

user_script.py

import mymodule
mymodule.set_freecad_path('/path/to/freecad/bin')

as mymodule needs to have FreeCAD available to start with in sys.path?

I tried a few things but not sure which is the most user friendly / best way to do it?

1. ask the user to sys.path.append() at the top of their script -- Is this good practice? This makes it hard for my code to tell whether the user has specified the path or whether it should default to finding it in the "usual suspect locations"

2. config.toml / .yaml / .ini -- This would be nice but if I eventually publish this to pypi and users just install it, how do I deal with software upgrades? The software default is to hardcode the version in the path, and is frequently updated.

Answer 1

To follow up on my comment...

There are several circumstances where imports within functions/classes can't really be avoided (if you look closely you'll find a lot of them even in the most popular packages).

If you need to delay the import until you know the location from which you want to import I think there's not really much you can do about it...

In my opinion, a pattern similar to this is "pythonic" enough and should do the job just fine (maybe also use pathlib for os-independent path specifications):

def _register_freecad(p=None):
    if p is not None and p not in sys.path:
        sys.path.append(p)

    try:
        import FreeCAD
    except ImportError:
        raise ImportError(f"{p} is not a valid path to the FreeCAD installation!")



class FreecadParametricFEA:
    def __init__(self, path=None):
        _register_freecad(path)