Range Enumerate.

Fifth class. for over a string or list yields the elements. Sometimes you also need the index.

range(n) yields 0, 1, …, n-1. It is often paired with len: for i in range(len(items)).

enumerate(items) yields (index, item) pairs. It is handy when you print both position and value:

for i, item in enumerate(items):
    print(i, item)

Mini example:

items = ["a", "b"]
for i in range(len(items)):
    print(i)
for i, item in enumerate(items):
    print(i, item)

Common mistake: starting range(len(items)) from 1; or swapping enumerate order (index comes first, then the value).