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To: python-list@python.org
From: Terry Reedy <tjreedy@udel.edu>
Subject: Re: Idioms combining 'next(items)' and 'for item in items:'
Date: Sun, 11 Sep 2011 20:45:41 -0400
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:13152

On 9/11/2011 6:41 PM, Chris Angelico wrote:
> On Mon, Sep 12, 2011 at 2:47 AM, Terry Reedy<tjreedy@udel.edu>  wrote:
>> What you are saying is a) that the following code
>>
>> for title in ['amazinG', 'a helL of a fiGHT', '', 'igNordEd']:
>>     print(fix_title(title))

> At least in Python 3.2, this isn't the case. StopIteration breaks the
> loop only if it's raised during the assignment, not during the body.

It breaks the loop *silently* only if ...

>>>> x=iter([1,2,3,4,5])
>>>> for i in x:
> 	print("%d - %d"%(i,next(x)))
>
> 1 - 2
> 3 - 4
> Traceback (most recent call last):
>    File "<pyshell#281>", line 2, in<module>
>      print("%d - %d"%(i,next(x)))
> StopIteration

whereas, you are right, it breaks it noisily in the body. So Ian's claim 
that StopIteration must be caught to avoid silent termination is not 
true. Thanks for pointing out what I saw but did not cognize the full 
implication of before. A better exception and an error message with an 
explaination might still be a good idea, though.

-- 
Terry Jan Reedy