On Tue, Aug 12, 2014 at 10:28:14AM +1000, Nick Coghlan wrote:
On 12 Aug 2014 09:09, "Allen Li" <cyberdupo56@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