Github-magic-merge-commit

def get_head_commit(self):
    with change_directory(self.get_config_dir() or os.getcwd()):
        stdout, stderr = run_shell_command('git log -1 --pretty=%B')

        stdout = stdout.rstrip('\n')
        pos = stdout.find('\n')
        shortlog = stdout[:pos] if pos != -1 else stdout

        magic_github_merge_commit_regex = re.compile(
            r'^Merge [0-9a-f]+ into [0-9a-f]+$|....')
        match = re.fullmatch(magic_github_merge_commit_regex, shortlog)

        if match and len(shortlog) == 92:
            command = 'git log --pretty=%P -n 1 ' + head_commit
            parent_commits = run_shell_command(command)
            sha_regex = re.compile(r'([0-9a-f]{40})')
            unmerged_commit_sha = re.findall(sha_regex, parent_commits)[1]

            command = ('git log -n 1 ' +
                       str(unmerged_commit_sha) + ' --pretty=%B')

            return run_shell_command(command)

        else:
            return run_shell_command('git log -1 --pretty=%B')