revert_shortlog_regex = re.compile('^Revert\s\"[\S+\s*]*\"')
        headline_regex = re.compile(
            '^This reverts commit [0-9a-f]{40}')
        sha_regex = re.compile(r'\b[0-9a-f]{40}\b')
        if not allow_revert_commits and revert_shortlog_regex.match(shortlog):

            reverted_shortlog = shortlog.lstrip('Revert ')

            if len(body) != 0:
                body = body.strip('\n')
                blankline = body.find('\n\n')
                headline = body[:blankline] if blankline != -1 else body

                if headline_regex.match(headline):
                    commit_sha = re.search(sha_regex, headline)
                    commit_sha = commit_sha.group(0)
                    command = 'git log -n 1 ' + str(commit_sha)
                    rstdout, rstderr = run_shell_command(command)

                    if rstderr:
                        self.err('git:', repr(stderr))
                        yield Result(self, 'Invalid revert commit.')

                    rstdout = rstdout.rstrip('\n')
                    rpos = rstdout.find('\n')
                    old_shortlog = rstdout[:rpos] if rpos != -1 else rstdout

                    if old_shortlog != reverted_shortlog:
                        yield Result(self, 'Shortlog of revert commit does \
                                            not match the original commit.')

                reason = body[blankline+1:] if blankline != -1 else ''

                if len(reason) == 0:
                    yield Result(self, 'Revert commit does not have a reason.')

                elif len(reason) > 50:
                    yield Result(self, 'Reason of revert commit contains too \
                                        long lines.')

            else:
                yield Result(self, 'Revert commit does not have a reason.')