For review: PEP 343: Anonymous Block Redux and Generator Enhancements

Steven Bethard steven.bethard at
Sat Jun 4 17:43:48 CEST 2005

Ilpo Nyyssönen wrote:
> How about this instead:
> with locking(mutex), opening(readfile) as input:
>     ...

I don't like the ambiguity this proposal introduces.  What is input 
bound to?  The return value of locking(mutex).__enter__() or the return 
value of opening(readfile).__enter__()?  Seems ambiguous to me.  And is 
the file opened with the mutex held, or not?  Sure, all of these 
questions can be answered with an arbitrary decision.  But the point is 
that, whatever decision you make, I now have to *memorize* that decision.

Note that if I wrote:

with locking(mutex):
     with opening(readfile) as input:

it's clear that input is the return value of 
opening(readfile).__enter__(), and that the mutex is held while the file 
is opened.  I don't need to memorize these things; they are explicit in 
the syntax.

I can see making the with-statement proposal more complex if you had 
some very good motivating examples for wanting the multiple-expressions 
extension.  But you have yet to provide a real-world use case.  Go 
search your codebase, and find some examples of where you would actually 
use this.  For the complexity that you want to add to the 
with-statement, you need to show that there's a *large* advantage to a 
*variety* of use cases in *real-world* code.


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