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1"""2Basic subprocess implementation for POSIX which only uses os functions. Only3implement features required by setup.py to build C extension modules when4subprocess is unavailable. setup.py is not used on Windows.5"""6import os7 8 9# distutils.spawn used by distutils.command.build_ext10# calls subprocess.Popen().wait()11class Popen:12    def __init__(self, cmd, env=None):13        self._cmd = cmd14        self._env = env15        self.returncode = None16 17    def wait(self):18        pid = os.fork()19        if pid == 0:20            # Child process21            try:22                if self._env is not None:23                    os.execve(self._cmd[0], self._cmd, self._env)24                else:25                    os.execv(self._cmd[0], self._cmd)26            finally:27                os._exit(1)28        else:29            # Parent process30            _, status = os.waitpid(pid, 0)31            self.returncode = os.waitstatus_to_exitcode(status)32 33        return self.returncode34 35 36def _check_cmd(cmd):37    # Use regex [a-zA-Z0-9./-]+: reject empty string, space, etc.38    safe_chars = []39    for first, last in (("a", "z"), ("A", "Z"), ("0", "9")):40        for ch in range(ord(first), ord(last) + 1):41            safe_chars.append(chr(ch))42    safe_chars.append("./-")43    safe_chars = ''.join(safe_chars)44 45    if isinstance(cmd, (tuple, list)):46        check_strs = cmd47    elif isinstance(cmd, str):48        check_strs = [cmd]49    else:50        return False51 52    for arg in check_strs:53        if not isinstance(arg, str):54            return False55        if not arg:56            # reject empty string57            return False58        for ch in arg:59            if ch not in safe_chars:60                return False61 62    return True63 64 65# _aix_support used by distutil.util calls subprocess.check_output()66def check_output(cmd, **kwargs):67    if kwargs:68        raise NotImplementedError(repr(kwargs))69 70    if not _check_cmd(cmd):71        raise ValueError(f"unsupported command: {cmd!r}")72 73    tmp_filename = "check_output.tmp"74    if not isinstance(cmd, str):75        cmd = " ".join(cmd)76    cmd = f"{cmd} >{tmp_filename}"77 78    try:79        # system() spawns a shell80        status = os.system(cmd)81        exitcode = os.waitstatus_to_exitcode(status)82        if exitcode:83            raise ValueError(f"Command {cmd!r} returned non-zero "84                             f"exit status {exitcode!r}")85 86        try:87            with open(tmp_filename, "rb") as fp:88                stdout = fp.read()89        except FileNotFoundError:90            stdout = b''91    finally:92        try:93            os.unlink(tmp_filename)94        except OSError:95            pass96 97    return stdout98