3.16 Boolean Operators and, or and not

Boolean Operator and

• Ensure that two conditions are both True with the Boolean and operator.

gender = 'Female'

age = 70

if gender == 'Female' and age >= 65:
    print('Senior female')

Senior female

• Truth table for the and operator:

expression1	expression2	expression1 and expression2
False	False	False
False	True	False
True	False	False
True	True	True

Boolean Operator or

• Ensure that one or both of two conditions are True with the Boolean or operator.

semester_average = 83

final_exam = 95

if semester_average >= 90 or final_exam >= 90:
    print('Student gets an A')

Student gets an A

• Truth table for the or operator:

expression1	expression2	expression1 or expression2
False	False	False
False	True	True
True	False	True
True	True	True

Improving Performance with Short-Circuit Evaluation

• Python stops evaluating an and expression as soon as it knows whether the entire condition is False.
• Python stops evaluating an or expression as soon as it knows whether the entire condition is True.
• In expressions that use and, make the condition that’s more likely to be False the leftmost condition.
• In or operator expressions, make the condition that’s more likely to be True the leftmost condition.

Boolean Operator not

• “Reverse” the meaning of a condition.
• Unary operator—it has only one operand.

grade = 87

if not grade == -1:
    print('The next grade is', grade)

The next grade is 87

if grade != -1:
    print('The next grade is', grade)

The next grade is 87

• Truth table for the not operator.

expression	not expression
False	True
True	False

• Precedence and grouping of the operators introduced so far—shown in decreasing order of precedence.

Operators	Grouping
()	left to right
**	right to left
*     /     //    %	left to right
+     -	left to right
<     <=     >     >=     ==     !=	left to right
not	left to right
and	left to right
or	left to right

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