python - 如何嵌套任意数量的 Python 文件上下文管理器？

Question

我想采用代表嵌套 tar 存档的任意数量的路径，并对最里面的存档执行操作。问题是，嵌套可以是任意的，所以我需要的上下文管理器的数量也是任意的。

举个例子:

ARCHIVE_PATH = "path/to/archive.tar"

INNER_PATHS = (
    "nested/within/archive/one.tar",
    "nested/within/archive/two.tar",
    # Arbitary number of these
)

def list_inner_contents(archive_path, inner_paths):
    with TarFile(archive_path) as tf1:
        with TarFile(fileobj=tf1.extractfile(inner_paths[0])) as tf2:
            with TarFile(fileobj=tf2.extractfile(inner_paths[1])) as tf3:
                # ...arbitary level of these!
                return tfX.getnames()

contents = list_inner_contents(ARCHIVE_PATH, INNER_PATHS))

我不能使用 with 语句的 nesting syntax因为可以嵌套任意数量的级别。我不能使用 contextlib.nested因为文档就在那里说:

...using nested() to open two files is a programming error as the first file will not be closed promptly if an exception is thrown when opening the second file.

有没有一种方法可以使用语言结构来执行此操作，或者我是否需要手动管理我自己的打开文件对象堆栈？

Answer 1

对于这种情况，您可以使用递归。对于这种情况感觉是最自然的(当然如果 Python 中还没有特殊处理的话):

ARCHIVE_PATH = "path/to/archive.tar"

INNER_PATHS = [
    "nested/within/archive/one.tar",
    "nested/within/archive/two.tar",
    # Arbitary number of these
]

def list_inner_contents(archive_path, inner_paths):
    def rec(tf, rest_paths):
        if not rest_paths:
            return tf.getnames()

        with TarFile(fileobj=tf.extractfile(rest_paths[0])) as tf2:
            return rec(tf2, rest_paths[1:])

    with TarFile(archive_path) as tf:
        try:
            return rec(tf, inner_paths)
        except RuntimeError:
            # We come here in case the inner_paths list is too long
            # and we go too deeply in the recursion
            return None