Gettext po file git merge driver

.gitattributes

*.po merge=pofile

3 .gitconfig

[merge "pofile"]
	name = custom merge driver for gettext po files
	driver = po-merge-driver.py %A %O %B

po-merge-driver.py

#!/usr/bin/env python3
import importlib
import subprocess
import sys

def default_merge_and_exit():
    print(f"running default git merge", file=sys.stderr)
    subprocess.run(['git', 'merge-file', '-L', 'ours', '-L', 'base', '-L', 'theirs', sys.argv[1], sys.argv[2], sys.argv[3]])
    exit(1)

# check if polib is available
try:
    import polib
except ModuleNotFoundError as err:
    print('polib is not installed', file=sys.stderr)
    default_merge_and_exit()

try:
    # create 3 dictionnaries
    ours={}
    for e in polib.pofile(sys.argv[1]):
        ours[e.msgid]=e.msgstr
    base={}
    for e in polib.pofile(sys.argv[2]):
        base[e.msgid]=e.msgstr
    theirs={}
    for e in polib.pofile(sys.argv[3]):
        theirs[e.msgid]=e.msgstr

    all_keys=set(ours.keys())
    all_keys.update(base.keys())
    all_keys.update(theirs.keys())

    # check for conflicts
    conflicts=[]
    for key in sorted(all_keys):
        presence = (key in ours, key in base, key in theirs)
        if presence == (False, True, True) and base[key] != theirs[key]:
            conflicts.append(f"key removed by us and modified by them : {key}")
        if presence == (True, True, False) and base[key] != ours[key]:
            conflicts.append(f"key removed by them and modified by us : {key}")
        if presence == (True, False, True) and ours[key] != theirs[key]:
            conflicts.append(f"key added by them and us in a different way : {key}")
        if presence == (True, True, True) and base[key] != ours[key] and base[key] != theirs[key] and ours[key] != theirs[key]:
            conflicts.append(f"key modified by them and us in a different way : {key}")
    if conflicts:
        print(f"\nERROR : automerge for {sys.argv[1]} will conflict :", file=sys.stderr)
        for c in conflicts:
            print(c, file=sys.stderr)
        print("\n", file=sys.stderr)
        default_merge_and_exit()

    # update ours_po, knowing that there are no conflicts
    ours_po=polib.pofile(sys.argv[1])

    # mutate all entries with their modifications
    for e in ours_po:
        key=e.msgid
        if key in theirs and key in base and theirs[key] != base[key]:
            e.msgstr = theirs[key]

    # remove all entries removed by them
    # mutate the object without creating a new one https://stackoverflow.com/a/1208792/436792
    ours_po[:] = [e for e in ours_po if e.msgid in theirs]

    # add all entries introduced by them
    theirs_po=polib.pofile(sys.argv[3])
    for e in theirs_po:
        key=e.msgid
        if key not in ours:
            ours_po.append(e)

    # save result
    ours_po.save(sys.argv[1])

    # format result
    formatted = subprocess.check_output(['msgcat', '--sort-output',sys.argv[1]], text=True)
    open(sys.argv[1], 'w').write(formatted)
except BaseException:
    default_merge_and_exit()