Traverse a list in reverse order in Python

Question

So I can start from collection[len(collection)-1] and end in collection[0].

I also want to be able to access the loop index.

Answer 1

You can do:

for item in my_list[::-1]:     print item 

(Or whatever you want to do in the for loop.)

The [::-1] slice reverses the list in the for loop (but won't actually modify your list "permanently").

Answer 2

Use the built-in reversed() function:

>>> a = ["foo", "bar", "baz"] >>> for i in reversed(a): ...     print(i) ...  baz bar foo 

To also access the original index, use enumerate() on your list before passing it to reversed():

>>> for i, e in reversed(list(enumerate(a))): ...     print(i, e) ...  2 baz 1 bar 0 foo 

Since enumerate() returns a generator and generators can't be reversed, you need to convert it to a list first.