On Tue, Aug 12, 2014 at 10:28:14AM +1000, Nick Coghlan wrote:
> On 12 Aug 2014 09:09, "Allen Li" <cyberdup...@gmail.com> wrote:
> >
> > This is a problem I sometimes run into when working with a lot of files
> > simultaneously, where I need three or more `with` statements:
> >
> > with open('foo') as foo:
> > with open('bar') as bar:
> > with open('baz') as baz:
> > pass
> >
> > Thankfully, support for multiple items was added in 3.1:
> >
> > with open('foo') as foo, open('bar') as bar, open('baz') as baz:
> > pass
> >
> > However, this begs the need for a multiline form, especially when
> > working with three or more items:
> >
> > with open('foo') as foo, \
> > open('bar') as bar, \
> > open('baz') as baz, \
> > open('spam') as spam \
> > open('eggs') as eggs:
> > pass
>
> I generally see this kind of construct as a sign that refactoring is
> needed. For example, contextlib.ExitStack offers a number of ways to manage
> multiple context managers dynamically rather than statically.
I don't think that ExitStack is the right solution for when you have a
small number of context managers known at edit-time. The extra effort of
writing your code, and reading it, in a dynamic manner is not justified.
Compare the natural way of writing this:
with open("spam") as spam, open("eggs", "w") as eggs, frobulate("cheese") as
cheese:
# do stuff with spam, eggs, cheese
versus the dynamic way:
with ExitStack() as stack:
spam, eggs = [stack.enter_context(open(fname), mode) for fname, mode in
zip(("spam", "eggs"), ("r", "w")]
cheese = stack.enter_context(frobulate("cheese"))
# do stuff with spam, eggs, cheese
I prefer the first, even with the long line.
--
Steven
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