3.3 Comparison
Comparisons
A Boolean value is a value that can only be True or False. It is called “Boolean” after the mathematician and logician George Boole
Boolean 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 |
Here are some more examples:
4 < 5
True
4 < 3
False
4 <= 4
True
Notice the == in the table above.
The double equals == is different from the single = that we saw before
in assignment. Here is assignment.
a = 4
Notice it does not display a value.
== is different - it’s a comparison operator like < or >. It checks
whether two values are equal, and returns True or False:
a == 4
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"
True
"Catastrophe" > "Cat"
True