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

Steven Bethard steven.bethard at gmail.com
Sun Jun 5 07:40:45 CEST 2005


Nicolas Fleury wrote:
> I prefer the optional-indentation syntax.  The reason is simple (see my 
> discussion with Andrew), most of the time the indentation is useless, 
> even if you don't have multiple with-statements.  So in my day-to-day 
> work, I would prefer to write:
> 
> def getFirstLine(filename):
>     with opening(filename) as file
>     return file.readline()
> 
> than:
> 
> def getFirstLine(filename):
>     with opening(filename) as file:
>         return file.readline()

One of the beauties of PEP 343 is that it can be explained simply in 
terms of current Python syntax.  The expression:

     with EXPR as VAR:
         BLOCK

is equivalent to:

     abc = EXPR
     exc = (None, None, None)
     VAR = abc.__enter__()
     try:
         try:
             BLOCK
         except:
             exc = sys.exc_info()
             raise
     finally:
         abc.__exit__(*exc)

Can you do the same thing for your proposal?  As I understand it you 
want some sort of implicitly-defined BLOCK that starts the line after 
the with statement and runs to the end of the current block...

Do you think the benefit of less indentation outweighs the added 
complexity of explaining the construct?  I still can't think of a good 
way of explaining the semantics you want.  If you could provide an 
explanation that's simple and as explicit as Guido's explanation in PEP 
343, I think that would help your case a lot.

STeVe

P.S.  I think it's a great sign that people are mainly squabbling about 
syntax here.  More likely than not, Guido's already made his mind up 
about the syntax.  So, since no one seems to have any real problems with 
the semantics, I'm hopeful that we'll get a direct implementation of PEP 
343 in the next Python release. =)



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