Question

我知道with语句在同一级别上支持多个上下文管理器，如下所示：

with open('foo.txt') as foo, open('bar.txt') as bar:
    do_something()

但是如果上下文管理器列表对于一行来说太长了怎么办？例如：

with open('foo.txt') as foo, open('bar.txt') as bar, open('bla.txt') as bla, open('yada.txt') as yada:
    do_something()

当前，这些是Python 3.7中的无效语法：

with (
    open('foo.txt') as foo,
    open('bar.txt') as bar,
    open('bla.txt') as bla,
    open('yada.txt') as yada, # same thing without the last trailing comma
):
    do_something()

with 
    open('foo.txt') as foo,
    open('bar.txt') as bar,
    open('bla.txt') as bla,
    open('yada.txt') as yada, # same thing without the last trailing comma
:
    do_something()

我可以做到：

foo = open('foo.txt')
bar = open('bar.txt')
bla = open('bla.txt')
yada = open('yada.txt')

with foo, bar, bla, yada:
    do_something()

但是随着我添加更多的上下文管理器，即使增长的时间也会太长。

我也可以这样做：

with open('foo.txt') as foo:
    with open('bar.txt' as bar:
        with open('bla.txt' as bla:
            with open('yada.txt') as yada:
                do_something()

但这很丑。它还缺乏对人类读者的语义提示。我们之所以要首先将多个上下文管理器放在同一级别上，是有原因的。

我知道很多上下文管理器属于同一级别是非常罕见的，但这绝对是可能的。

Answer 1

续行是您的朋友在这里...

with \
    open('foo.txt') as foo, \
    open('bar.txt') as bar, \
    open('bla.txt') as bla, \
    open('yada.txt') as yada \
:
    do_something()

这实际上在PEP-8中有专门提及。

在Python中将多个相同级别的上下文管理器拆分为多行

1 个答案: