Boolean expressions#

Boolean expressions are expressions in Python programming language that produces a boolean value when evaluated. The value can either be True or False. In Python, False maps to 0 (zero) and True maps to 1 (one). Boolean operations are used to control the flow of a program and make a comparison. Python also provides the bool() function, which allows you to cast other types to True or False.

This can be shown in the expressions below:

one = 1
two = 2
print(one == two)

False

When you want to compare two values in Python, you need to use comparisons operator == instead of a single =. A single = is known as the assignment operator, as was mentioned in previous chapters. It assigns the value on the right to the variable on the left.

What is False and True?#

Almost any value is evaluated to True if it has:

  • Any string is True, except empty strings.

  • Any number is True, except 0.

  • Any list, tuple, set, and dictionary are True, except empty ones.

The following values are False:

  • 0 (integer, float or complex)

  • Empty collections: “ ”, (), [], {}

  • None type

Comparisons Operator#

In Python programming, the comparison operator is used to compare two values and evaluate them down to a single value that can either be one or zero or rather True or False. Boolean is a subclass of the int class. There are several boolean operators that can be used to evaluate an expression as either True or False.

These expressions include:

  • Equals: ==

  • Not Equals: !=

  • Less than: <

  • Less than or equal to: <=

  • Greater than: >

  • Greater than or equal to: >=

x = 5
y = 10

print(x == y)  # Is 5 equal to 10?
print(x != y)  # Is 5 not equal to 10?

False
True

Logical operator#

Logical operators are operators that are used to compare two values and the final expression is evaluated down to a boolean value True or False. These logical operations are given in the table below:

  • and

  • not

  • or

print((10 > 5) and (2 < 4))
print((3 > 5) and (2 < 4))  

True
False

For AND operator, both expressions must evaluate to True for the final boolean expression to be True else the final boolean value will be False.

Logic AND Truth Table

Expressions

Result

True and True

True

True and False

False

False and True

False

False and False

False

For the OR operator, at least one of the two operators must evaluate to True for the final boolean expression to evaluate to True.

print((10 > 5) or (2 < 4))
print((2 > 5) or (5 < 4)) 

True
False

Logic OR Truth Table

Expressions

Result

True or True

True

True or False

True

False or True

True

False or False

False

OR operation can evaluate to False only, if both operations evaluate to False.

Lastly, NOT is the opposite of False and True which means, its inner expression is True for the new expression to evaluate to False else it will evaluate to True.

Logic NOT Truth Table

Expressions

Result

not True

False

not False

True

Expressions consist of values and operators, and they can always evaluate (that is, reduce) down to a single value.