“with"语句中的多个变量? [英] Multiple variables in a 'with' statement?

问题描述

是否可以在 Python 中使用 with 语句声明多个变量?

Is it possible to declare more than one variable using a with statement in Python?

类似于:

from __future__ import with_statement

with open("out.txt","wt"), open("in.txt") as file_out, file_in:
    for line in file_in:
        file_out.write(line)

...还是同时清理两个资源的问题?

... or is cleaning up two resources at the same time the problem?

推荐答案

可以在 Python 3 自 v3.1 和 Python 2.7.新的with 语法支持多个上下文管理器:

It is possible in Python 3 since v3.1 and Python 2.7. The new with syntax supports multiple context managers:

with A() as a, B() as b, C() as c:
    doSomething(a,b,c)

与 contextlib.nested 不同，这保证了 a 和 b 将拥有它们的 __exit__()'即使 C() 或其 __enter__() 方法引发异常，也会调用 s.

Unlike the contextlib.nested, this guarantees that a and b will have their __exit__()'s called even if C() or it's __enter__() method raises an exception.

您还可以在以后的定义中使用以前的变量(h/t Ahmad 下面):

You can also use earlier variables in later definitions (h/t Ahmad below):

with A() as a, B(a) as b, C(a, b) as c:
    doSomething(a, c)

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