在 python 中，一行中的多个“with”语句是否等同于嵌套的“with”语句？

Question

这两个语句等价吗？

with A() as a, B() as b:
  # do something

with A() as a:
  with B() as b:
    # do something

我问是因为 a 和 b 都改变了全局变量（此处为 tensorflow）并且 b 取决于 a 所做的更改。所以我知道第二种形式可以安全使用，但是是否相当于将其缩短为第一种形式？

Answer 1

是的，根据 Python 2.7 language reference:

，在一行中列出多个 with 语句与嵌套它们完全相同

With more than one item, the context managers are processed as if multiple with statements were nested:
with A() as a, B() as b:
    suite
is equivalent to
with A() as a:
    with B() as b:
        suite

完全相同的语言出现在Python 3 language reference。

Answer 2

完全相同。就看个人喜好了。

Answer 3

正如其他人所说，这是相同的结果。下面是有关如何使用此语法的更详细示例：

blah.txt

我可以打开一个文件并将其内容以简洁的方式写入另一个文件：

with open('blah.txt', 'r') as infile, open('foo.txt', 'w+') as outfile:
    for line in infile:
        outfile.write(str(line))

foo.txt 现在包含：

在 python 中，一行中的多个“with”语句是否等同于嵌套的“with”语句？

Are multiple `with` statements on one line equivalent to nested `with` statements, in python?

python

with-statement