[Python-ideas] with None (Was: Re: Enhanced context managers with ContextManagerExit and None)

[Serhiy Storchaka]

13.08.13 18:04, Masklinn написав(ла):
> Please note that enter_context will return the result of
> object.__enter__, so:
>
> with contextlib.ExitStack() as cm:
>      file = cm.enter_context(open(path1)) if condition1 else None
>      file2 = cm.enter_context(open(path2)) if condition2 else None
>      process(file, file2, ...)

Well, it works. However there are two disadvantages:

1. You need import contextlib.

2. cm.enter_context() increases a length of already long lines so you 
need split lines.

N.B. Currently ExitStack used only in two places in stdlib (and I am the 
originator of both changes). In most cases it is simpler to do without 
ExitStack.