Comparisons

Boolean (True or False) values most often arise from comparison operators. Python includes a variety of operators that compare values. For example, 3 is larger than 1 + 1.

3 > 1 + 1

True

The value True indicates that the comparison is valid; Python has confirmed this simple fact about the relationship between 3 and 1+1. The full set of common comparison operators are listed below.

Comparison	Operator	True example	False Example
Less than	<	2 < 3	2 < 2
Greater than	>	3>2	3>3
Less than or equal	<=	2 <= 2	3 <= 2
Greater or equal	>=	3 >= 3	2 >= 3
Equal	==	3 == 3	3 == 2
Not equal	!=	3 != 2	2 != 2

An expression can contain multiple comparisons, and they all must hold in order for the whole expression to be True. For example, we can express that 1+1 is between 1 and 3 using the following expression.

1 < 1 + 1 < 3

True

The average of two numbers is always between the smaller number and the larger number. We express this relationship for the numbers x and y below. You can try different values of x and y to confirm this relationship.

x = 12
y = 5
min(x, y) <= (x+y)/2 <= max(x, y)

True

Strings can also be compared, and their order is alphabetical. A shorter string is less than a longer string that begins with the shorter string.

"Dog" > "Catastrophe" > "Cat"

True

in and not in

While not exactly comparing two quantities, you can check to see if a string is contained within another string using the operators in and not in in. As is always the case with strings, these operations are case-sensitive.

'hello' in 'hello world'

True

'a' not in 'apple'

False

'app' in 'apple'

True

'D' in 'dog'

False

This will be a useful tool to check to see if a specific letter, word, or phrase is contained within a string that is storing a message.