Is there a way to loop through a sub section of a list in Python

So for a list that has 1000 elements, I want to loop from 400 to 500. How do you do it?

I don't see a way by using the for each and for range techniques.

From stackoverflow

• for element in allElements[400:501]:
       # do something
  

  These are slices and generate a sublist of the whole list. They are one of the main elements of Python.

  Joan Venge : Thanks. So this will include both 400th and 500th elements?

  Georg : Only if the upper bound is 501.

• for x in thousand[400:500]:
      pass
  

  If you are working with an iterable instead of a list, you should use itertools:

  import itertools
  for x in itertools.islice(thousand, 400, 500):
      pass
  

  If you need to loop over thousand[500], then use 501 as the latter index. This will work even if thousand[501] is not a valid index.

  J.F. Sebastian : It's worth mentioning that `alist[istart:iend]` creates a completely new list with a shallow copy of all elements from `alist` between `istart` and `iend` indices. It is a O(iend-istart) operation.

• Using

  for element in allElements[400:501]:
      doSomething(element)
  

  makes Python create new object, and might have some impact on memory usage.

  Instead I'd use:

  for index in xrange(400, 501):
      doSomething(allElements[index])
  

  This way also enables you to manipulate list indexes during iteration.

  EDIT: In Python 3.0 you can use range() instead of xrange(), but in 2.5 and earlier versions range() creates a list while xrange() creates a generator, which eats less of your precious RAM.