3. Comparisons¶
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 |
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