README.md

Usage is simply

VERSION_PATH=<package name> python <(curl -Ls https://bit.ly/set__version__)

This will set the __version__ variable in <package name/__init__.py based on either the VERSION or GITHUB_REF environment variables.

set__version__.py

#!/usr/bin/env python3
"""
see https://gist.github.com/samuelcolvin/e49096dc93396be60d2e972e8799410d for details
"""
import os
import re
import sys
from pathlib import Path

version_regex = re.compile(r'^(__version__ ?= ?).+$', flags=re.M)


def main(version_path_env_var='VERSION_PATH', version_env_vars=('VERSION', 'GITHUB_REF')) -> str:
    version_path = os.getenv(version_path_env_var)
    if not version_path:
        return f'✖ "{version_path_env_var}" env variable not found'

    version_path = Path(version_path)
    if version_path.is_dir():
        version_path = version_path / '__init__.py'

    if not version_path.is_file():
        return f'✖ "{version_path}" file does not exist'

    version = None
    for var in version_env_vars:
        version_ref = os.getenv(var)
        if version_ref:
            version = re.sub('^refs/tags/v*', '', version_ref.lower())
            break

    if not version:
        return f'✖ "{version_env_vars}" env variables not found'

    content = version_path.read_text()
    if not version_regex.search(content):
        return f'✖ "{version_path}" does not contain a "__version__ = ..." line'

    content = re.sub(version_regex, fr"\1'{version}'", content)

    print(f'✔ writing version "{version}", to {version_path}')
    version_path.write_text(content)


if __name__ == '__main__':
    err = main()
    if err:
        print(err, file=sys.stderr)
        sys.exit(1)