2.11 Loops

We use a loop to repeat some action or set of actions while a condition is true.

2.11.1 while

Suppose we want to know the sum of the positive integers less than or equal to 5. This is not much work for you to type and compute directly.

1 + 2 + 3 + 4 + 5

15

Now suppose you want the sum of the positive integers less than or equal to 500. That’s certainly more than you or I would want to type! We can do it easily with a while loop.

sum, count = 0, 1

while count <= 500:
    sum += count
    count += 1

sum

125250

We initialize sum and count and then increment sum by count and count by one while count is less than or equal to 500.

Exercise 2.16

What does Python do if you forget to include count += 1?

Let me make the problem smaller and insert a print call so we can see what is happening.

sum, count = 0,...