Mixing Boolean and Comparison Operators

As we studied the Comparison Operators and Boolean Values in the recent units, it's time to introduce a kind of operators that can be applied on Boolean values as well, the Boolean Operators. They are used to compare Boolean values. The types of operators are and, or and not.

Binary Boolean Operators

and and or are binary Boolean operators. That means they operate on two values, the evaluated values need to be either True or False.

The and operator evaluates an expression to be True if both Boolean values are True; otherwise, it evaluates to False.

>>> True and False
False
>>> True and True
True

A truth table shows every possible result of a Boolean operator.

Truth table for and operator:

Expression	Evaluates to
True `and` True	True
True `and` False	False
False `and` True	False
False `and` False	False

The or operator is quite interesting. 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.

>>> True or False
True
>>> False or False
False

Truth table for or operator:

Expression	Evaluates to
True `or` True	True
True `or` False	True
False `or` True	True
False `or` False	False

NOT Operator

Unlike the other two operators, not operator simply evaluates the opposite Boolean value. not is a unary operator which means it operates on one value only.

Truth table for not operator:

Expression	Evaluates to
`not` True	False
`not` False	True

Boolean and Comparison Operators

Now that you have a basic understanding of what's going on here, lets move to the main topic. To put this in a nutshell, since the comparison operators evaluate to Boolean values, you can use them in expressions with the Boolean operators. To break it down further, 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.

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 refer to the examples for this purpose.

Here are some examples:

>>> (3 < 5) and (5 < 8)
True
>>> (4 < 5) and (9 < 6)
False
>>> (1 == 3) or (2 == 2)
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 evaluates to True.

Mixing Boolean and Comparison Operators