Boolean Operators [Python]

The three Boolean operators (and, or, and not) are used to compare Boolean values. Like comparison operators, they evaluate these expressions down to a Boolean value. Let’s explore these operators in detail, starting with the and operator.

Boolean Operators [Python]

Binary Boolean Operators

The and and or operators always take two Boolean values (or expressions), so they’re considered binary operators. The and operator evaluates an expression to True if both Boolean values are True; otherwise, it evaluates to False.

Enter some expressions using and into the interactive shell to see it in action.

A truth table shows every possible result of a Boolean operator. The truth table for the and operator.

The and Operator’s Truth Table

On the other hand, the or operator evaluates an expression to True if either of the two Boolean values is True. If both are False, it evaluates to False.

>>> False or TrueTrue>>> False or FalseFalse

You can see every possible outcome of the or operator in its truth table, shown in Table:

The or Operator’s Truth Table

The not Operator
Unlike and and or, the not operator operates on only one Boolean value (or expression). The not operator simply evaluates to the opposite Boolean value.

>>> not TrueFalse

>>> not not not not TrueTrue

Much like using double negatives in speech and writing, you can nest not operators u, though there’s never not no reason to do this in real programs.

The Table will shows the truth table for not.

The not Operator’s Truth Table

Mixing Boolean and Comparison Operators
Since the comparison operators evaluate to Boolean values, you can use
them in expressions with the Boolean operators.
Recall that the and, or, and not operators are called Boolean operators
because they always operate on the Boolean values True and False. While
expressions like 4 < 5 aren’t Boolean values, they are expressions that evaluate
down to Boolean values. Try entering some Boolean expressions that
use comparison operators into the interactive shell.

>>> (4 < 5) and (5 < 6)True>>> (4 < 5) and (9 < 6)False>>> (1 == 2) or (2 == 2)True

The computer will evaluate the left expression first, and then it will evaluate the right expression. When it knows the Boolean value for each, it will then evaluate the whole expression down to one Boolean value. You can think of the computer’s evaluation process for (4 < 5) and (5 < 6) as shown in Figure below.

The

process of evaluating

(4 < 5) and

(5 < 6) to True.

You can also use multiple Boolean operators in an expression, along with the comparison operators.

>>> 2 + 2 == 4 and not 2 + 2 == 5 and 2 * 2 == 2 + 2 True

The Boolean operators have an order of operations just like the math operators do. After any math and comparison operators evaluate, Python evaluates the not operators first, then the and operators, and then the or operators.

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