标准库中 sublcas 的重写方法无法在模块中找到名称

Question

我正在尝试 subprocess.Popen 的子类中的一个方法，即它的 _execute_child 方法：

class MyPopen(Popen):

    def _execute_child(self, args, executable, preexec_fn, close_fds,
                           pass_fds, cwd, env,
                           startupinfo, creationflags, shell,
                           p2cread, p2cwrite,
                           c2pread, c2pwrite,
                           errread, errwrite,
                           unused_restore_signals,
                           unused_gid, unused_gids, unused_uid,
                           unused_umask,
                           unused_start_new_session):
            """Execute program (MS Windows version)"""

            assert not pass_fds, "pass_fds not supported on Windows."

            if isinstance(args, str):
                pass
            elif isinstance(args, bytes):
                if shell:
                    raise TypeError('bytes args is not allowed on Windows')
                args = list2cmdline([args])
            elif isinstance(args, os.PathLike):
                if shell:
                    raise TypeError('path-like args is not allowed when '
                                    'shell is true')
                args = list2cmdline([args])
            else:
                args = list2cmdline(args)

            if executable is not None:
                executable = os.fsdecode(executable)

            # Process startup details
            if startupinfo is None:
                startupinfo = STARTUPINFO()
            else:
                # bpo-34044: Copy STARTUPINFO since it is modified above,
                # so the caller can reuse it multiple times.
                startupinfo = startupinfo.copy()

            use_std_handles = -1 not in (p2cread, c2pwrite, errwrite)
            if use_std_handles:
                startupinfo.dwFlags |= _winapi.STARTF_USESTDHANDLES
                startupinfo.hStdInput = p2cread
                startupinfo.hStdOutput = c2pwrite
                startupinfo.hStdError = errwrite

            attribute_list = startupinfo.lpAttributeList
            have_handle_list = bool(attribute_list and
                                    "handle_list" in attribute_list and
                                    attribute_list["handle_list"])

            # If we were given an handle_list or need to create one
            if have_handle_list or (use_std_handles and close_fds):
                if attribute_list is None:
                    attribute_list = startupinfo.lpAttributeList = {}
                handle_list = attribute_list["handle_list"] = \
                    list(attribute_list.get("handle_list", []))

                if use_std_handles:
                    handle_list += [int(p2cread), int(c2pwrite), int(errwrite)]

                handle_list[:] = self._filter_handle_list(handle_list)

                if handle_list:
                    if not close_fds:
                        warnings.warn("startupinfo.lpAttributeList['handle_list'] "
                                      "overriding close_fds", RuntimeWarning)

                    # When using the handle_list we always request to inherit
                    # handles but the only handles that will be inherited are
                    # the ones in the handle_list
                    close_fds = False

            if shell:
                startupinfo.dwFlags |= _winapi.STARTF_USESHOWWINDOW
                comspec = os.environ.get("COMSPEC", "cmd.exe")
                args = '{} /c "{}"'.format (comspec, args)

            if cwd is not None:
                cwd = os.fsdecode(cwd)

            sys.audit("subprocess.Popen", executable, args, cwd, env)

            # Start the process
            try:
                hp, ht, pid, tid = _winapi.CreateProcess(executable, args,
                                         # no special security
                                         None, None,
                                         int(not close_fds),
                                         creationflags,
                                         env,
                                         cwd,
                                         startupinfo)
            finally:
                # Child is launched. Close the parent's copy of those pipe
                # handles that only the child should have open.  You need
                # to make sure that no handles to the write end of the
                # output pipe are maintained in this process or else the
                # pipe will not close when the child process exits and the
                # ReadFile will hang.
                self._close_pipe_fds(p2cread, p2cwrite,
                                     c2pread, c2pwrite,
                                     errread, errwrite)

            # Retain the process handle, but close the thread handle
            self._child_created = True
            self._handle = Handle(hp)
            self.pid = pid
            _winapi.CloseHandle(ht)

但是当我尝试创建 suclass 的实例时，它会抛出 list2cmdline 和 _winapi 的 NameErrors。这些是在标准库 subprocess.py 模块中定义的，那么为什么类找不到它们呢？

当我导入 from subprocess import * 时，这些对 sublcas 不可用吗？

Answer 1

如果您阅读了 subprocess< 的 源代码 /code>，您会看到 list2cmdline 和 _winapi 未包含在 __all__ 中（这是模块控制导出哪些符号的方式） 。

__all__ = ["Popen", "PIPE", "STDOUT", "call", "check_call", "getstatusoutput",
           "getoutput", "check_output", "run", "CalledProcessError", "DEVNULL",
           "SubprocessError", "TimeoutExpired", "CompletedProcess"]
           # NOTE: We intentionally exclude list2cmdline as it is
           # considered an internal implementation detail.  issue10838.

您应该在代码中显式导入 _winapi，因为模块不会导出它，并且可能也会将 list2cmdline 实现复制到您的代码中。