Why is the PATH changed when Windows PyQt5 is imported?

[Barry Scott]

I'm debugging an issue that is breaking some of my code.
I'm using Python 3.8 and PyQt5==5.12.2

What I'm seeing is that the PATH is changed by PyQt5 __init__.py.

It has this code in it:

---
import os as _os

_path = _os.path.dirname(__file__) + '\\Qt\\bin;' + _os.environ['PATH']
_os.environ['PATH'] = _path
---

Why is this necessary?

Its has the effect that any subprocess created from a PyQt5 program
gets this PATH.

And if a program that uses a different version of PyQt5 then the
one the PATH has at its start sees DLL errors.

Is this a because of the change in 3.8 for DLL loading?
Should this code use the os.add_dll_directory instead?

Why am I spotting this now? I've changed my build processes to use
a venv. I have installed tools that use an older PyQt5 and then
build the updated tools using the venv.

Barry