How can I use enumerate to count backwards?

Question

letters = ['a', 'b', 'c']

Assume this is my list. Where for i, letter in enumerate(letters) would be:

0, a
1, b
2, c

How can I instead make it enumerate backwards, as:

2, a
1, b
0, c

Answer 1

This is a great solution and works perfectly:

items = ['a', 'b', 'c', 'd', 'e', 'f', 'g']
for idx, item in enumerate(items, start=-len(items)):
    print(f"reverse index for {item}: {abs(idx)}")

Here is the OUTPUT of the above snippet:

reverse index for a: 7
reverse index for b: 6
reverse index for c: 5
reverse index for d: 4
reverse index for e: 3
reverse index for f: 2
reverse index for g: 1

Here is what happening in above snippet:

• enumerate's start arg is given a negative value.
• enumerate always takes a step forward.
• Finally we use abs on idx to find absolute value, which is always positive.
• If you want to start indexing from zero then use -len(items) + 1 to fix off-by-one error