python for loop, how to find next value(object)?

Question

HI, I\'m trying to use for loop to find the difference between every two object by minus each other. So, how can I find the next value in a for loop?

for ent         


        

Answer 1

zip works for lists, but for the general case:

def pairs(it):
    it = iter(it)
    prev = next(it)
    for v in it:
        yield prev, v
        prev = v

a = [1,2,3,4,5]
for prev, cur in pairs(a):
    print cur - prev

import itertools as it
for prev, cur in pairs(it.cycle([1,2,3,4])):
    print cur - prev

This works efficiently for large containers, and more importantly, it works for iterators:

for prev, cur in pairs(open("/usr/share/dict/words").xreadlines()):
    print cur, prev,

Edit: I changed the generator to omit the first value with no previous value, since that fits the original question better ("finding differences between adjacent pairs"), and I added an example case showing that it works for an infinitely-repeating iterator.