snakile snakile - 19 days ago 5
Python Question

How to loop backwards in python?

I'm talking about doing something like:

for(i=n; i>=1; --i) {
//do something with i
}


I can think of some ways to do so in python (creating a list of
range(1,n+1)
and reverse it, using
while
and
--i
, ...) but I wondered if there's a more elegant way to do it. Is there?

EDIT:
Some suggested I use xrange() instead of range() since range returns a list while xrange returns an iterator. But in Python 3 (which I happen to use) range() returns an iterator and xrange doesn't exist.

Answer

range() and xrange() take a third parameter that specifies a step. So you can do the following.

range(10, 0, -1)

Which gives

[10, 9, 8, 7, 6, 5, 4, 3, 2, 1] 

But for iteration, you should really be using xrange instead. So,

xrange(10, 0, -1)
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