4.7: Conditional Expressions

Learning Objectives

By the end of this section you should be able to

• Identify the components of a conditional expression.
• Create a conditional expression.

Conditional expressions

A conditional expression (also known as a "ternary operator") is a simplified, single-line version of an if-else statement.

Conditional expression template:

    expression_if_true if condition else expression_if_false

A conditional expression is evaluated by first checking the condition. If condition is true, expression_if_true is evaluated, and the result is the resulting value of the conditional expression. Else, expression_if_false is evaluated, and the result is the resulting value of the conditional expression.

A variable can be assigned with a conditional expression. Ex: Finding the max of two numbers can be calculated with max_num = y if x < y else x

Note: Conditional expressions have the lowest precedence of all Python operations.

Checkpoint: Example: Version check

Concepts in Practice \(\PageIndex{1}\): Using conditional expressions

What is the conditional expression version of the following if-else statement?

if x%2 == 0:
  response = 'even'
else:
  response = 'odd'

1. response = if x%2 == 0 "even" else "odd"
2. response = "odd" if x%2 == 0 else "even"
3. response = "even" if x%2 == 0 else "odd"

Answer

c. The conditional expression will assign response with "even" if x is even. response is assigned with "odd" if x is odd.

Concepts in Practice \(\PageIndex{2}\): Using conditional expressions

Given x = 100 and offset = 10, what is the value of result?

result = x + offset if x < 100 else x - offset

1. 90
2. 100
3. 110

Answer

a. 100 < 100 is False so result is assigned with x - offset = 100 - 10 = 90.

Concepts in Practice \(\PageIndex{3}\): Using conditional expressions

Which part of the conditional expression is incorrect?

min_num = x if x < y else min_num = y

1. min_num = x
2. x < y
3. min_num = y

Answer

c. min_num cannot be assigned with min_num = y. The correct expression is min_num = x if x < y else y"

Concepts in Practice \(\PageIndex{4}\): Using conditional expressions

Which of the following is an improved version of the following if-else statement?

if x < 50:
  result = True
else:
  result = False

1. result = True if x < 50 else False
2. result = x < 50

Answer

b. Conditional expressions that evaluate to a Boolean are redundant. The Boolean expression should be used instead.

Concepts in Practice \(\PageIndex{5}\): Using conditional expressions

What are the possible values of total?

total = fee + 10 if hours > 12 else 2

1. 10, 2
2. fee + 10, 2
3. fee + 10, fee + 2

Answer

b. The expression is evaluated as (fee + 10) if hours > 12 else 2. So if hours > 12, the result will be fee + 10; otherwise, the result will be 2.

Try It: Ping values

Write a program that reads in an integer, ping, and prints ping_report, a string indicating whether the ping is low to average or too high. ping values under 150 have a ping_report of "low to average". ping values of 150 and higher have a ping_report of "too high". Use a conditional expression to assign ping_report.

Ex: If the input is 30, the output is "Ping is low to average".

Interactive Code

Input

150

Answer

ping = int(input())
ping_report = "low to average" if ping < 150 else "too high"

print("Ping is", ping_report)