for loop question

Steven D'Aprano steve at
Thu Oct 11 05:40:19 CEST 2007

On Wed, 10 Oct 2007 20:25:00 +0000, Paul Hankin wrote:

>> A "works-for-me":
>>  >>> pairs = (test[i:i+2] for i in xrange(len(test)-1))
>>  >>> for a,b in pairs:
>>  ...     print a,b
> for a, b in zip(test, test[1:]):
>   print a, b

May be unfortunately slow if test is half a gigabyte of data, what with 
essentially making three copies of it. Lazy procedures like the generator 
expression above are often much better.

Just for completion, here's another way:

prev = test[0]
for i in xrange(1, len(test)):
    print prev, test[i]
    prev = test[i]


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