A Concise Introduction to Programming in Python

Chapter 4

Repetition: For Loops

To this point, our Python programs have been limited to tasks that could be

accomplished by a calculator. Repetition, the ability to rep eat any section

of a program, adds a surprising amount of new power.

Listing 4.1: Harmonic Sum

1 # harmonic.py

2

3 def harmonic(n):

4 # Compute the sum of 1/k for k=1 to n.

5 total = 0

6 for k in range(1, n + 1):

7 total += 1 / k

8 return total

9

10 def main():

11 n = int(input(’Enter a positive integer: ’))

12 print("The sum of 1/k for k = 1 to", n, "is", harmonic(n))

13

14 main()

This program computes the harmonic sum

1 +

1

2

+

1

3

+

1

4

+ ···+

1

n

=

n

∑

k=1

1

k

Type it in and run it a few times to get a feeling ...