Hello,
I tried to extend our config processing using the environment variables and the configparser module. 

On some machines (all windows) the configparser failed with an InterpolationSyntaxError ...
It seems that not resolved environment variables (e.g. "test":"%not_existing%") lead to this error.
I wrote little python test file reproducing the error and providing a very simple workaround to not fix all environments ;) Attention the bug is reproduced but the test is green ^^

I would be happy to remove the workaround as soon as possible ;)

The exception is due to the interpolation feature of ConfigParser, which expects a different syntax. The default interpolation syntax is "%(key)s".

Interpolation can be turned off by passing "interpolation=None" when creating the ConfigParser object.

See also https://docs.python.org/3/library/configparser.html#interpolation-of-values

So I have to use two config parser objects to merge the configuration of one config.ini (needs interpolation) and the environment on windows ?

So at the end choose wether to use environment variables or config parser interpolation, right? (only on windows) 

Not the solution I was looking for.

There's multiple options:

1. Escape '%' in environment variables (%%not_existing%%) to avoid the exception

2. Switch to configparser.ExtendedInterpolation for the interpolation, which uses a different syntax that doesn't conflict with env. variables on Windows (but does conflict with that on Unix)

Note that regardless of the option ConfigParser will not expand the value of the environment variable reference. If you want to be able to interpolate env variables you need a different solution, for example by using the 'defaults' argument to ConfigParser and expand references using the ConfigParser interpolation syntax.

Thanks a lot for the fast response ... did not expect this ;)
I have looked into many threads and I will try to implement my own interpolation to use the current basic interpolation and process the current environment.

So thanks a lot, stay healthy and have a nice day!