#Boolean search generator code

> True or print_and_true () True > False or print_and_true () print_and_true called True The following examples demonstrate the short-circuit evaluation of or: If the first argument is True, then the result is True, and there is no need to evaluate the second argument. If both inputs are True, then the result of or is True.īecause it uses an inclusive or, the or operator in Python also uses short-circuit evaluation. When Python interprets the keyword or, it does so using the inclusive or.

For example, “If you do well on this task, then you can get a raise and/or a promotion” means that you might get both a raise and a promotion. The inclusive or is sometimes indicated by using the conjunction and/or. The exclusive or is how or is used in the phrase “You can file for an extension or submit your homework on time.” In this case, you can’t both file for an extension and submit your homework on time. When used informally, the word or can have one of two meanings: This table is verbose, but it has the same meaning as the explanation above. Once the second input was evaluated, inverse_and_true(0) would be called, it would divide by 0, and an exception would be raised. In that case, the value of the second input would be needed for the result of and. In contrast, True and inverse_and_true(0) would raise an exception. Because of short-circuit evaluation, the function isn’t called, the division by 0 doesn’t happen, and no exception is raised. However, the last line doesn’t raise an exception. It does serve the purpose of neatly failing when given 0 as a parameter since division by 0 is invalid. The function inverse_and_true() is admittedly silly, and many linters would warn about the expression 1 // n being useless. > inverse_and_true ( 5 ) True > inverse_and_true ( 0 ) Traceback (most recent call last):įile '', line 2, in inverse_and_true ZeroDivisionError: integer division or modulo by zero > False and inverse_and_true ( 0 ) False

#Boolean search generator code

In the most extreme cases, the correctness of your code can hinge on the short-circuit evaluation. In other cases, such as when it would be computationally intensive to evaluate expressions that don’t affect the result, it provides a significant performance benefit. In some cases, it might have little effect on your program. The importance of short-circuit evaluation depends on the specific case. In those cases, the other input is not evaluated. These specifications are called truth tables since they’re displayed in a table.Īs you’ll see later, in some situations, knowing one input to an operator is enough to determine its value. Since Python Boolean values have only two possible options, True or False, it’s possible to specify the operators completely in terms of the results they assign to every possible input combination. You’ll see how this generalizes to other values in the section on truthiness. For now, all examples will use Boolean inputs and results. Note: Later, you’ll see that these operators can be given other inputs and don’t always return Boolean results.

Boolean Operatorsīoolean operators are those that take Boolean inputs and return Boolean results. This is a useful way to take advantage of the fact that Booleans are numbers. The word 'the' appears in half the lines in the selection. Now, if you divide that result by 4, the length of the list, you get 0.5. When you add False + True + True + False, you get 2. Since is a list of four Booleans, you can add them together. Since Booleans are numbers, you can add them to numbers, and 0 + False + True gives 1. In the second line, 'the' does appear, so 'the' in line_list is True. The first line doesn’t have the word 'the' in it, so 'the' in line_list is False. The line_list variable holds a list of lines. splitlines () > 'the' in line_list False > 'the' in line_list True > 0 + False + True # Equivalent to 0 + 0 + 1 1 > False + True + True + False 2 > len ( line_list ) 4 > 2 / 4 0.5