Boolean Expressions

A boolean expression makes a comparison and returns one of the boolean values, either True or False.

To make a decision within our code, a boolean expression is used as the condition. A condition is a comparison that can be called correct (True) or incorrect (False).

Testing for Equality

The equality operator, ==, compares two values and returns True or False depending on whether the values are identical.

Example

1
2
3
4
5
6
num = 37
other_num = 40

print(5 == 5)
print('abc' == 'def')
print(num == other_num - 3)

Console Output

True
False
True

In line 4, the two values are equal, so the expression evaluates to True. In line 5, the string 'abc' is not equal to 'def', so we get False. Line 7 compares the result of other_num - 3 with the value stored in num.

Tip

A common error is using a single equals sign (=) instead of a double equals (==) when comparing two values. We call = an assignment operator, but == is a comparison operator.

To set the value of a variable, use = (e.g. name = 'Mae').
To compare values, use == (e.g. name == other_name).

An equality test is symmetric, meaning that we can switch the places of the two values and get the same result. If num == 7 is True, then 7 == num is also True. However, an assignment statement is not symmetric. num = 7 works while 7 = num does not.

Other Comparisons

The == operator is one of seven common comparison operators.

Note

Remember: The values on either side of an operator are called operands.

Operator	Description	Example Returning `True`	Example Returning `False`
Equal (`==`)	Returns `True` if two compared operands are equal, and `False` otherwise.	`7 == 3 + 4`	`7 == 5`
Not equal (`!=`)	Returns `True` if two operands are NOT equal, and `False` otherwise.	`7 != 5`	`7 != 7`
Greater than (`>`)	Returns `True` if the left-hand operand is greater than the right-hand operand, and `False` otherwise.	`7 > 5`	`7 > 7`
Less than (`<`)	Returns `True` if the left-hand operand is less than the right-hand operand, and `False` otherwise.	`5 < 7`	`15 < 15`
Greater than or equal (`>=`)	Returns `True` if the left-hand operand is greater than or equal to the right-hand operand, and `False` otherwise.	`7 >= 5`	`5 >= 7`
Less than or equal (`<=`)	Returns `True` if the left-hand operand is less than or equal to the right-hand operand, and `False` otherwise.	`5 <= 7`	`7 <= 5`
`in`	Returns `True` if the left-hand operand is found inside the right-hand operand, and `False` otherwise. This operator does not work for the `int` or `float` data types.	`'a' in 'Happy'`	`'A' in 'apple'` (case matters)

Check Your Understanding

Question

Which of the following are boolean expressions? Select ALL that apply.

3 <= 4
3 + 4
"DogCat" == "dog" + "cat"
"False"
text = 'Rutabagas!'