1.3.6 Boolean expressions

A Boolean expression is an expression that has the value True or False. Some common operators that yield conditional expressions are as follow:

•  Equal: ==
•  Not equal: !=
•  Strictly less, less  or equal: <, <=
•  Strictly greater, greater or equal: >, >=

You combine different Boolean values with or and and. The keyword not gives the logical negation of the expression that follows. Comparisons can be chained so that, for example, x < y < z is equivalent to x < y and y < z. The difference is that y is only evaluated once in the first example. In both cases, z is not evaluated at all when the first condition, x < y, evaluates to False:

2 >= 4 # False 
2 < 3 < 4 # True 
2 < 3 and 3 < 2 # False 
2 != 3 < 4 or False # True 
2 <= 2 and 2 >= 2 # True 
not 2 == 3 # True...