Which is the best way to allow configuration options be overridden at the command line in Python?

Question

I have a Python application which needs quite a few (~30) configuration parameters. Up to now, I used the OptionParser class to define default values in the app itself, with

Answer 1

fromfile_prefix_chars

Maybe not the perfect API, but worth knowing about.

main.py

#!/usr/bin/env python3
import argparse
parser = argparse.ArgumentParser(fromfile_prefix_chars='@')
parser.add_argument('-a', default=13)
parser.add_argument('-b', default=42)
print(parser.parse_args())

Then:

$ printf -- '-a\n1\n-b\n2\n' > opts.txt
$ ./main.py
Namespace(a=13, b=42)
$ ./main.py @opts.txt
Namespace(a='1', b='2')
$ ./main.py @opts.txt -a 3 -b 4
Namespace(a='3', b='4')
$ ./main.py -a 3 -b 4 @opts.txt
Namespace(a='1', b='2')

Documentation: https://docs.python.org/3.6/library/argparse.html#fromfile-prefix-chars

Tested on Python 3.6.5, Ubuntu 18.04.