Loops, comprehensions and enumerate

for, while, range, zip and list comprehensions - plus when a comprehension is the wrong choice.

11 min read · Lesson 4 of 6 · Pro

Python's for loop is not C's for loop

C's loop is a counter: start, condition, step. Python's for walks over the items of a collection directly.

Python 3

marks = [72, 65, 88]

for m in marks:
    print(m)

There is no index. You asked for the items, so you get the items. When you genuinely need a counter, range makes one.

Python 3

for i in range(5):        # 0 1 2 3 4
    print(i)

for i in range(1, 6):     # 1 2 3 4 5
    print(i)

for i in range(10, 0, -2):  # 10 8 6 4 2
    print(i)

range(a, b) stops before b. That is deliberate: range(0, n) gives exactly n values, and range(0, 5) plus range(5, 10) covers 0 to 9 with no gap and no overlap.

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