Changing version of App Engine application on checkout to a git branch

It’s very common and useful to use current branch name (or something dependent on it) as a version for App Engine application. And it’s painful and error-prone to change it manually.

It’s easily can be automatized with a git hook, we just need to fill .git/hooks/post-checkout with something like:

#!/usr/bin/env python
import glob
import subprocess

def get_yaml_paths():
    """Returns all `.yaml` files where `version` can be changed."""
    for path in glob.glob('*.yaml'):
        with open(path) as yml:
            content =
            if 'version:' in content:
                yield path

def get_version():
    """Returns `version`, currently just current branch."""
    proc = subprocess.Popen(['git', 'rev-parse', '--abbrev-ref', 'HEAD'],

def replace_version(path, new_version):
    with open(path, 'r') as yml:
        lines = yml.readlines()
    with open(path, 'w') as yml:
        for line in lines:
            if line.startswith('version'):
                yml.write('version: {}\n'.format(new_version))

version = get_version()
print("Change version in yaml files to", version)
for path in get_yaml_paths():
    replace_version(path, version)

And make it executable:

chmod +x .git/hooks/post-checkout

In action:

➜ cat app.yaml | grep "^version:"
version: fixes
➜ git checkout feature
Switched to branch 'feature'
Your branch is up-to-date with 'origin/feature'.
Change version in yaml files to feature
➜ cat app.yaml | grep "^version:"
version: feature

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