Loops Are Fun (You Can Say That Again) 63

if one of them is greater or less than the other, or if they are equal

or not equal. Is x less than 7? Yes or no? True or False? Based on

the result, True or False, you can tell your program to run different

pieces of code.

The while loop shares some features with the for loop. First,

like the for loop, it repeats a set of statements over and over as

needed. Second, with both while loops and for loops, we tell Python

which statements to repeat by indenting them to the right with the

tab key.

Let’s try a program with a while loop to see it in action. Type

the following code (or download it from http://www.nostarch.com/

teachkids/), and run it:

SayOurNames.py

Ask the user for their name

u name = input("What is your name? ")

Keep printing names until we want to quit

v while name != "":

Print their name 100 times

w for x in range(100):

Print their name followed by a space, not a new line

x print(name, end = " ")
y print() # After the for loop, skip down to the next line

Ask for another name, or quit

z name = input("Type another name, or just hit [ENTER] to quit: ")
{ print("Thanks for playing!")

We begin the program by asking the user their name at u and

storing their answer in the variable name. We need a name to test as

the condition of our while loop, so we have to ask once before the loop

starts. Then, at v, we start our while loop, which will run as long as

the name the user enters is not an empty string (represented by two

double quotes with nothing between them: ""). The empty string is

what Python sees as the input when the user presses enter to quit.

At w, we start our for loop, which will print the name

100 times, and at x, we tell the print() statement to print a space

after the name each time. We’ll keep going back to w and checking

to see if x has reached 100, then printing at x until the name fills

a few lines of the screen. When our for loop has finished printing

the name 100 times, we print a blank line without a space y, mov-

ing the printout down to the next clear line. Then, it’s time to ask

for another name z.