[Python-ideas] "Iteration stopping" syntax [Was: Is this PEP-able? for X in ListY while conditionZ:]

[Shane Green]

Yes, but it only works for generator expressions and not comprehensions.  My opinion of that workaround is that it’s also a step backward in terms of readability.  I suspect 

if i < 50 else stop() would probably also work, since it throws an exception.  That’s better, IMHO.  






On Jun 28, 2013, at 6:38 PM, Andrew Carter <acarter at g.hmc.edu> wrote:

> Digging through the archives (with a quick google search) http://mail.python.org/pipermail/python-ideas/2013-January/019051.html, if you really want an expression it seems you can just do
> 
> def stop():
>   raise StopIteration
> list(i for i in range(100) if i < 50 or stop())
> 
> it seems to me that this would provide syntax that doesn't require lambdas.
> 
> 
> 
> 
> 
> 
> On Fri, Jun 28, 2013 at 4:50 PM, Alexander Belopolsky <alexander.belopolsky at gmail.com> wrote:
> 
> 
> 
> On Fri, Jun 28, 2013 at 7:38 PM, Shane Green <shane at umbrellacode.com> wrote:
> ..
> [x until condition for x in l ...] or 
> [x for x in l until condition]
> 
> Just to throw in one more variation:
> 
> [expr for item in iterable break if condition]
> 
> (inversion of "if" and "break"reinforces the idea that we are dealing with an expression rather than a statement - compare with "a if cond else b")  
> 
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