[Python-ideas] Nested with statements

Pascal Chambon chambon.pascal at wanadoo.fr
Tue Apr 28 21:59:25 CEST 2009

> spir a écrit :
>> Le Mon, 27 Apr 2009 20:54:58 +0100,
>> Arnaud Delobelle <arnodel at googlemail.com> s'exprima ainsi:
>>>> with A(), B() as a,b:
>>>>    # Code that uses a and b.
>>>> This would translate directly to:
>>>> with A() as a:
>>>>    with B() as b:
>>>>        # Code that uses a and b.  
>>> There was a discussion about this on this list:
>>> http://mail.python.org/pipermail/python-ideas/2009-March/003188.html
>>> I can't remember the outcome.
>> There was no clear outcome, for sure ;-)
>> Except maybe it was stated that 
>>    with A(), B() as a,b:
>> should rather be spelled
>>    with A() as a, B() as b:
>> to reuse the syntax of imports.
>> Denis
>> ------
>> la vita e estrany
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I agree with the idea of auto-nesting "with", however in the case you 
pointed out, the main problem was the early evaluation of context 
managers ;
maybe a solution would be to delay the creation of context managers, 
with something like a partial application (cf functools).

Roughly, we'd need a "delayedNested" function, which takes zero-argument 
callables as parameters, and calls/instanciates them inside itself.

Then just call* delayedNested(partial(A,...arguments...), partial(B, 
...arguments...))*/ /to have what you want.

Yes I know, it's not pretty (mainly because of the lack of partial 
application syntax in python), but it's just a placeholder ^^

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