Python ConfigParser .ini parsing and portable variable substitutions

Question

I want to have a .ini entry that references special variables e.g.

[magic_module]
magic_directory: ${env:PWD}/magic

currently, I have the non-portable

[magic_module]
magic_directory: C:/Users/user1/projects/project1/magic

I would like to have a .ini path entry that is more portable instead of hard-coded to my computer. Does the Python ConfigParser natively perform substitutions like this?

This is slightly different than SO question ConfigParser and String interpolation with env variable because I am wondering about any possible default interpolated variables, not just environment variables.

This is for passing information to a different module (mypy) that uses ConfigParser.

Specifically, this is for improving portability in a Python package. I'm trying to set the mypy_path within a mypy.ini while working with a pipenv-created virtualenv python environment. The user install module paths will change so I want to portably set that for mypy.

Using Python 3.7.

Possible duplicate of ConfigParser and String interpolation with env variable — CryptoFool
– CryptoFool, Commented Feb 24, 2019 at 6:06
Maybe I am misunderstand something in my experience I found that: a) .env-files + pipenv run + os.environ or b) .env-files + python-dotenv solves all my needs. Both solutions are quite portable. Do I miss something? — Alex Yu
– Alex Yu, Commented Feb 25, 2019 at 3:00

Sau001 · Accepted Answer · 2024-04-10 20:29:46Z

By setting the parameter value interpolation to an instance of the class ExtendedInterpolation you can meet your objective. See example below. This is tested on Python 3.9.7.

sample.ini

In the following example, I am:

referencing the Windows out of box environment variable WINDIR via interpolation.
Further, I am also cross referencing a config items across sections.

[magic_module]
magic_directory: ${WINDIR}/magic

[another_section]
another_directory=${magic_module:magic_directory}\folder1\folder2

main.py

import configparser
import os

def display_setting(config: configparser.ConfigParser,section: str, key: str):
    value=config.get(section, key)
    print(f"Value of {section}:{key}={value}")

print("Begin....")
config = configparser.ConfigParser(os.environ, interpolation=configparser.ExtendedInterpolation())
sample_ini_file=os.path.join(os.path.dirname(__file__),"sample.ini")
print(f"Going to load the INI file {sample_ini_file}")
config.read(sample_ini_file)

display_setting(config=config, section="magic_module", key="magic_directory")
display_setting(config=config, section="another_section", key="another_directory")

Output

Begin....
Going to load the INI file C:\work\sample.ini   
Value of magic_module:magic_directory=C:\WINDOWS/magic
Value of another_section:another_directory=C:\WINDOWS/magic\folder1\folder2

Link to documentation

https://docs.python.org/3.9/library/configparser.html#interpolation-of-values

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