A Concise Introduction to Programming in Python

Chapter 8

Repetition: While Loops

While loops allow programs to repeat without necessarily knowing ahead of

time how many times the loop will run. Like selection, this allows programs

to adapt and run more or less code, depending on the circumstances.

Consider the task of printing a table of prime numbers. An integer n is prime

if it is greater than 1 and its only positive divisors are 1 and itself. This

definition leads to the following program:

Listing 8.1: Prime Numbers

1 # primes.py

2

3 def isprime(n):

4 # Return True if n is prime.

5 return n > 1 and smallestdivisor(n) == n

6

7 def smallestdivisor(n):

8 # Find smallest divisor (other than 1) of integer ...