What is the best way in Python to loop over a list back to front?

Question

Right now I do it like this:

for i in range(len(my_list)-1, -1, -1):
    # ...

but I am wondering if we have a better way with clearer meaning.

Answer 1

Use the reversed() function :

for elem in reversed(my_list):

An object can support efficient reverse iteration by offering a __reversed__() special method ; list objects implement this method to support reverse iteration efficiently. Otherwise, the normal sequence protocol ( object.__getitem__() and object.__len__() ) must be implemented.

Note that this doesn't create a new list object; it produces an iterator , an object that tracks position in the list as you loop over it.