[Python-ideas] with statement: multiple context manager

[Guido van Rossum]

On Sun, Mar 1, 2009 at 1:35 PM, Chris Rebert <pyideas at rebertia.com> wrote:
> On Sun, Mar 1, 2009 at 12:57 PM, Christian Heimes <lists at cheimes.de> wrote:
>> Chris Rebert wrote:
>>> While I still mostly like the idea, it does seem to undermine Python's
>>> uniformity a bit.
>>
>> I played with both possible versions before I wrote the proposal. Both
>> ways have their pros and cons. I'm preferring the proposed way::
>>
>>  with a, b as x, d as y:
>>       ...
>>
>> over the other possibility::
>>
>>  with a, b, c as _, x, y:
>>      ...
>
> You misunderstand me. My quibble isn't over the exact syntax (in fact,
> I completely agree about the superiority of the proposed ordering),
> but rather that we're introducing syntax to do something that can
> already be done with a function (nested()) and is /extremely/ similar
> to another case (parallel for-loop) where we are opting to still
> require the use of a function (zip()). This proposed asymmetry
> concerns me.

Hm. While we can indeed write the equivalent of the proposed "with a,
b:" today as "with nested(a, b):", I don't think that the situation is
quite comparable to a for-loop over a zip() call. The nested() context
manager isn't particularly intuitive to me (and Nick just found a
problem in a corner case of its semantics). Compared to nested(), I
find "with a, b:" very obvious as a shorthand for nested
with-statements:

  with a:
    with b:
      ...

-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)