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Comparisons

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.