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""" 
Basic subprocess implementation for POSIX which only uses os functions. Only 
implement features required by setup.py to build C extension modules when 
subprocess is unavailable. setup.py is not used on Windows. 
""" 
import os 
 
 
# distutils.spawn used by distutils.command.build_ext 
# calls subprocess.Popen().wait() 
class Popen: 
    def __init__(self, cmd, env=None): 
        self._cmd = cmd 
        self._env = env 
        self.returncode = None 
 
    def wait(self): 
        pid = os.fork() 
        if pid == 0: 
            # Child process 
            try: 
                if self._env is not None: 
                    os.execve(self._cmd[0], self._cmd, self._env) 
                else: 
                    os.execv(self._cmd[0], self._cmd) 
            finally: 
                os._exit(1) 
        else: 
            # Parent process 
            _, status = os.waitpid(pid, 0) 
            self.returncode = os.waitstatus_to_exitcode(status) 
 
        return self.returncode 
 
 
def _check_cmd(cmd): 
    # Use regex [a-zA-Z0-9./-]+: reject empty string, space, etc. 
    safe_chars = [] 
    for first, last in (("a", "z"), ("A", "Z"), ("0", "9")): 
        for ch in range(ord(first), ord(last) + 1): 
            safe_chars.append(chr(ch)) 
    safe_chars.append("./-") 
    safe_chars = ''.join(safe_chars) 
 
    if isinstance(cmd, (tuple, list)): 
        check_strs = cmd 
    elif isinstance(cmd, str): 
        check_strs = [cmd] 
    else: 
        return False 
 
    for arg in check_strs: 
        if not isinstance(arg, str): 
            return False 
        if not arg: 
            # reject empty string 
            return False 
        for ch in arg: 
            if ch not in safe_chars: 
                return False 
 
    return True 
 
 
# _aix_support used by distutil.util calls subprocess.check_output() 
def check_output(cmd, **kwargs): 
    if kwargs: 
        raise NotImplementedError(repr(kwargs)) 
 
    if not _check_cmd(cmd): 
        raise ValueError(f"unsupported command: {cmd!r}") 
 
    tmp_filename = "check_output.tmp" 
    if not isinstance(cmd, str): 
        cmd = " ".join(cmd) 
    cmd = f"{cmd} >{tmp_filename}" 
 
    try: 
        # system() spawns a shell 
        status = os.system(cmd) 
        exitcode = os.waitstatus_to_exitcode(status) 
        if exitcode: 
            raise ValueError(f"Command {cmd!r} returned non-zero " 
                             f"exit status {exitcode!r}") 
 
        try: 
            with open(tmp_filename, "rb") as fp: 
                stdout = fp.read() 
        except FileNotFoundError: 
            stdout = b'' 
    finally: 
        try: 
            os.unlink(tmp_filename) 
        except OSError: 
            pass 
 
    return stdout