3.1.2.2 Loops in Python | while
The while loop: more examples
Let's look at another example employing the
while loop. Follow the comments to find out the idea and the solution.# A program that reads a sequence of numbers
# and counts how many numbers are even and how many are odd.
# The program terminates when zero is entered.
odd_numbers = 0
even_numbers = 0
# read the first number
number = int(input("Enter a number or type 0 to stop: "))
# 0 terminates execution
while number != 0:
# check if the number is odd
if number % 2 == 1:
# increase the odd_numbers counter
odd_numbers += 1
else:
# increase the even_numbers counter
even_numbers += 1
# read the next number
number = int(input("Enter a number or type 0 to stop: "))
# print results
print("Odd numbers count:", odd_numbers)
print("Even numbers count:", even_numbers)
Certain expressions can be simplified without changing the program's behavior.
Try to recall how Python interprets the truth of a condition, and note that these two forms are equivalent:
while number != 0: and while number:.
The condition that checks if a number is odd can be coded in these equivalent forms, too:
if number % 2 == 1: and if number % 2:.Using a counter variable to exit a loop
Look at the snippet below:
counter = 5
while counter != 0:
print("Inside the loop.", counter)
counter -= 1
print("Outside the loop.", counter)
This code is intended to print the string
"Inside the loop." and the value stored in the counter variable during a given loop exactly five times. Once the condition has not been met (the counter variable has reached 0), the loop is exited, and the message "Outside the loop."as well as the value stored in counter is printed.
But there's one thing that can be written more compactly - the condition of the
while loop.
Can you see the difference?
counter = 5
while counter:
print("Inside the loop.", counter)
counter -= 1
print("Outside the loop.", counter)
Is it more compact than previously? A bit. Is it more legible? That's disputable.
REMEMBER
Don't feel obliged to code your programs in a way that is always the shortest and the most compact. Readability may be a more important factor. Keep your code ready for a new programmer.
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