gistfile1.txt

#!/usr/bin/env python3

import re
from subprocess import check_output
from typing import Iterator


class BadCommitEx(Exception):

    def __init__(self, log_line):
        (sha1, author, subject) = log_line.split(None, 2)
        super().__init__(
            'Top commit does not appear to be a Bors merge. '
            f'SHA1={sha1}, Author="{author}", Subject="{subject}"')


def parse_pr_numbers_from_bors_merge() -> Iterator[int]:
    cmd = "git log --format='%h %an %s' -1"
    log_line = check_output(cmd, text=True, shell=True).strip()

    parts = log_line.split()
    if parts[1:3] != ['bors[bot]', 'Merge']:
        raise BadCommitEx(log_line)

    pr_parts = parts[3:]
    if not pr_parts:
        raise BadCommitEx(log_line)

    for pr_str in pr_parts:
        match = re.match(r'#(\d+)', pr_str)
        if not match:
            raise BadCommitEx(log_line)
        yield int(match.group(1))


for pr_num in parse_pr_numbers_from_bors_merge():
    print(pr_num)