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

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Concepts in Practice: Using conditional expressions

1.

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"

response = "odd" if x%2 == 0 else "even"

response = "even" if x%2 == 0 else "odd"

2.

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

3.

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

4.

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

5.

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

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".

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