A common scenario where you may use the
len() in combination with
for loop is when you want to change a list as it is being traversed.
Let’s add 1 to every item in the list
L1. A simple
for loop won’t work.
To change the list as you go throught it, we need to use indexes so we can assign an updated value to each position as we go.
len() in combination can produce the required indexes.
>>> L1 = [1, 2, 3] >>> for l in range(len(L1)): ... L1[l] += 1 ... >>> L1 [2, 3, 4]
for loop iterates through actual items, not list positions. A
while loop can achieve the same result but requires a bit more work and might run more slowly.
>>> L1 = [1, 2, 3] >>> l = 0 >>> while l < len(L1): ... L1[l] += 1 ... l += 1 ... >>> L1 [2, 3, 4]