在 Python 中处理多个文件时如何避免嵌套“with”语句

当使用推荐的样式在 Python 中处理多个文件时，代码可能会变得丑陋：

with open("foo.txt") as foo:
    with open("bar.txt", "w") as bar:
         with open("baz.txt", "w") as baz:
              # Read from foo, write different output to bar an baz

这是三个缩进级别，仅用于处理文件！另一种选择是这样的

foo = open("foo.txt")
bar = open("bar.txt", "w")
baz = open("baz.txt", "w")
# Read from foo, write different output to bar an baz
foo.close()
bar.close()
baz.close()

我有一种感觉，这两个例子都可以重构为更优雅的东西。有什么例子吗？

Python 2.7 及更高版本允许您在一个中指定多个上下文管理器with陈述：

with open("foo.txt") as foo, open("bar.txt", "w") as bar, open("baz.txt", "w") as baz:
    # Read from foo, write different output to bar an baz

线路does太长，并且不能使用括号将其保持在 80 个字符以下。您可以使用\然而反斜杠继续：

with open("foo.txt") as foo,\
        open("bar.txt", "w") as bar,\
        open("baz.txt", "w") as baz:
    # Read from foo, write different output to bar an baz

或者您可以将换行符放在“open()”调用的括号内：

with open(
    "foo.txt"
) as foo, open(
    "bar.txt", "w"
) as bar, open(
    "baz.txt", "w"
) as baz:
    # Read from foo, write different output to bar an baz

从 Python 3.10 开始，通过添加以下内容，这变得更加容易对多项目上下文管理器的括号支持:

with (
    open("foo.txt") as foo,
    open("bar.txt", "w") as bar,
    open("baz.txt", "w") as baz,
):
    # Read from foo, write different output to bar an baz

另一种选择是使用contextlib.ExitStack()上下文管理器（仅适用于 Python 3.3 及更高版本）：

from contextlib import ExitStack

with ExitStack() as stack:
    foo = stack.enter_context(open("foo.txt"))
    bar = stack.enter_context(open("bar.txt"))
    baz = stack.enter_context(open("baz.txt"))