How to traverse a list in reverse order in Python (index-style: '... in range(...)' only)

Question

I'm new to Python so I am still getting used to looping in this language. So, for example, I have the following code (the element type in the list is array)

my_list = [array0, array1, array2, array3]
temp = my_list[-1]
for k in range(len(my_list) - 1, 0):
    temp = temp + my_list[k - 1]
return temp

I want to traverse the list from the end of the list and stop at the second element (k=1), but it looks like the for loop will never be entered and it will just return the initial temp outside the loop. I don't know why. Can someone help? Thanks.

Answer 1

Avoid looping with range, just iterate with a for loop as a general advice.

If you want to reverse a list, use reversed(my_list).

So in your case the solution would be:

my_list = reversed([array0,array1,array2,array3])

That gives you [array3, array2, ...]

For omitting the last array from the reversed list, use slicing:

my_list = reversed([array0,array1,array2,array3])[:-1]

So your code turns to a one liner :-)

Answer 2

You can traverse a list in reverse like so:

for i in range(len(lis), 0, -1):
    print (i)

To stop at the second element edit your range() function to stop at 1:

for i in range(len(lis), 1, -1):
        print (i)