os.py 文件源码

def _fwalk(topfd, toppath, topdown, onerror, follow_symlinks):
        # Note: This uses O(depth of the directory tree) file descriptors: if
        # necessary, it can be adapted to only require O(1) FDs, see issue
        # #13734.

        names = listdir(topfd)
        dirs, nondirs = [], []
        for name in names:
            try:
                # Here, we don't use AT_SYMLINK_NOFOLLOW to be consistent with
                # walk() which reports symlinks to directories as directories.
                # We do however check for symlinks before recursing into
                # a subdirectory.
                if st.S_ISDIR(stat(name, dir_fd=topfd).st_mode):
                    dirs.append(name)
                else:
                    nondirs.append(name)
            except FileNotFoundError:
                try:
                    # Add dangling symlinks, ignore disappeared files
                    if st.S_ISLNK(stat(name, dir_fd=topfd, follow_symlinks=False)
                                .st_mode):
                        nondirs.append(name)
                except FileNotFoundError:
                    continue

        if topdown:
            yield toppath, dirs, nondirs, topfd

        for name in dirs:
            try:
                orig_st = stat(name, dir_fd=topfd, follow_symlinks=follow_symlinks)
                dirfd = open(name, O_RDONLY, dir_fd=topfd)
            except OSError as err:
                if onerror is not None:
                    onerror(err)
                continue
            try:
                if follow_symlinks or path.samestat(orig_st, stat(dirfd)):
                    dirpath = path.join(toppath, name)
                    yield from _fwalk(dirfd, dirpath, topdown, onerror, follow_symlinks)
            finally:
                close(dirfd)

        if not topdown:
            yield toppath, dirs, nondirs, topfd