Idioms combining 'next(items)' and 'for item in items:'

Chris Angelico rosuav at gmail.com
Mon Sep 12 00:41:05 CEST 2011


On Mon, Sep 12, 2011 at 2:47 AM, Terry Reedy <tjreedy at 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.

>>> 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

Compare with:

>>> def pair(it):
	while True:
		yield next(it),next(it)

>>> x=iter([1,2,3,4,5])
>>> for i,j in pair(x):
	print("%d - %d"%(i,j))

1 - 2
3 - 4

In this case, the StopIteration bubbles up and quietly terminates the loop.

ChrisA



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