4.1: Boolean Values

Learning Objectives

By the end of this section you should be able to

• Explain a Boolean value.
• Use bool variables to store Boolean values.
• Demonstrate converting integers, floats, and strings to Booleans.
• Demonstrate converting Booleans to integers, floats, and strings.
• Use comparison operators to compare integers, floats, and strings.

bool data type

People often ask binary questions such as yes/no or true/false questions. Ex: Do you like pineapple on pizza? Ex: True or false: I like pineapple on pizza. The response is a Boolean value, meaning the value is either true or false. The bool data type, standing for Boolean, represents a binary value of either true or false. true and false are keywords, and capitalization is required.

Checkpoint: Example: Crosswalk sign

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Concepts in Practice: Using Boolean variables

Consider the following code:

    is_fruit = "True"
    is_vegetable = 0
    is_dessert = False

1.

What is the data type of is_fruit?

1. Boolean

integer

string

2.

What is the data type of is_vegetable?

1. Boolean
2. integer
3. string

3.

What is the data type of is_dessert?

1. Boolean
2. integer
3. string

4.

How many values can a Boolean variable represent?

1. 2
2. 4
3. 8

5.

Which is a valid value for a Boolean variable?

1. true
2. True
3. 1

6.

Suppose the following is added to the code above:

is_dessert = 0
print(type(is_dessert))

What is the output?

1. <class 'bool'>
2. <class 'int'>
3. Error

Type conversion with bool()

Deciding whether a value is true or false is helpful when writing programs/statements based on decisions. Converting data types to Booleans can seem unintuitive at first. Ex: Is "ice cream" True? But the conversion is actually simple.

bool() converts a value to a Boolean value, True or False.

• True: any non-zero number, any non-empty string
• False: 0, empty string

Checkpoint: Converting integers, floats, and strings using bool()

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Concepts in Practice: Converting numeric types and strings to Booleans

7.

bool(0.000)

1. True

False

8.

bool(-1)

1. True
2. False

9.

bool("")

1. True
2. False

10.

bool("0")

1. True
2. False

11.

Given input False, what is bool(input())?

1. True
2. False

Concepts in Practice: Converting Booleans to numeric types and strings

Given is_on = True, what is the value of each expression?

12.

float(is_on)

1. 0.0

1.0

13.

str(is_on)

1. "is_on"
2. "True"

14.

int(is_on)

1. 0
2. 1

Comparison operators

Programmers often have to answer questions like "Is the current user the admin?" A programmer may want to compare a string variable, user, to the string, "admin". Comparison operators are used to compare values, and the result is either true or false. Ex: is_admin = (user == "admin"). user is compared with "admin" using the == operator, which tests for equality. The Boolean variable, is_admin, is assigned with the Boolean result.

The 6 comparison operators:

• equal to: ==
• not equal to: !=
• greater than: >
• less than: <
• greater than or equal to: >=
• less than or equal to: <=

Checkpoint: Example: Rolling a d20 in a tabletop game

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Concepts in Practice: Comparing values

For each new variable, what is the value of compare_result?

15.

x = 14
compare_result = (x <= 13)

1. True

False

16.

w = 0
compare_result = (w != 0.4)

1. True
2. False

17.

v = 4
compare_result = (v < 4.0)

1. True
2. False

18.

y = 2
compare_result = (y > "ab")

1. True
2. False
3. Error

19.

z = "cilantro"
compare_result = (z == "coriander")

1. True
2. False

20.

a = "dog"
compare_result = (a < "cat")

1. True
2. False

= vs ==

A common mistake is using = for comparison instead of ==. Ex: is_zero = num=0 will always assign is_zero and num with 0, regardless of num's original value. The = operator performs assignment and will modify the variable. The == operator performs comparison, does not modify the variable, and produces True or False.

Exploring further

• Unicode Basic Latin Chart

Try It: Friday Boolean

"It's Friday, I'm in love" —from "Friday I'm in Love," a song released by the Cure in 1992.

Write a program that reads in the day of the week. Assign the Boolean variable, in_love, with the result of whether the day is Friday or not.

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Try It: Even numbers

Write a program that reads in an integer and prints whether the integer is even or not. Remember, a number is even if the number is divisible by 2. To test this use number % 2 == 0. Ex: If the input is 6, the output is "6 is even: True".

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