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 + 1TrueThe 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 < 3TrueThe 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)TrueStrings 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"Truein 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'FalseThis 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.