The and Operator

00:00 The and operator is one of only two binary Boolean operators in Python. Binary means that the operator takes in two inputs. In Python, to apply the and operator to the inputs x and y, you simply type x and y.

00:17 and returns True only when both operands, or both inputs, evaluate to True.

00:24 Here is the truth table to the and operator.

00:29 There are only four possible inputs to the and operator, and the and operator will return only True when both of the inputs have a value of True.

00:41 In all other cases, and will return False.

00:46 There’s another way to think about how the and operator works, and we can divide those into two cases. The first case corresponds to when the first input to the and operator is True.

00:59 These are two cases, or two sub-cases. In these two cases, the return value of the and operator is completely determined by the value of the second input. So notice that in this case, the value of the output of the and operator is just simply the value to the second input. Again, this is provided that the first input has a value of True. Then, the output to and is just simply the value of the second input.

01:31 The other main case is when the first input to the and operator has a value of False. In these two sub-cases, the output to the and operator is False. So in these two sub-cases, the value of the second input plays no role.

01:50 These two cases correspond to and’s short-circuiting feature. The idea is that when and sees that the first input is False, it is going to immediately return False and it won’t matter what the second input is. In the upcoming examples, you’ll see how you can take advantage of this short-circuiting feature of the and operator.

02:14 Although Boolean operators are, by definition, supposed to return Boolean values, Python’s and operator returns the value of one of its operands.

02:26 The return value of the and operator is determined by and’s truth table. So when Python sees the expression x and y, the first input x is evaluated. If the Boolean value of x is False, or if x is falsy, then the value of x is returned.

02:46 This case corresponds to the short-circuiting feature of and, and corresponds to the last two rows of the truth table to the and operator.

02:56 However, if the first input x is True, then the second input y is evaluated and the resulting value of y is returned. This case corresponds to the first two rows of the truth table, and so this is the case where the value of the and operator is completely determined by the second input—in this case, y. You’ll see how the short-circuiting feature of the and operator can be used to shorten your code or to set default values.

03:27 It can also be used to make your program more computationally efficient. If in an and operator expression the first input is False, then the second input doesn’t have to be evaluated and you can save some computational time.

03:41 You’ll see an example of this in the upcoming code.

03:46 Let’s start off by generating the truth table of the and operator. But instead of doing this manually, let’s use the product() function in the itertools module.

03:56 So go ahead and import from the itertools module the product() function.

04:02 If you’re not familiar with the product() function, I’ll let you look it up but we’re going to use it to generate all four inputs to the and operator.

04:12 Go ahead and type for x, y in and then we’re going to have the product() of the list that contains both of the Boolean values, True and False.

04:24 And then we’re going to pass on a keyword argument of repeat, and so what this will do is generate the Cartesian product of the list containing both True and False.

04:35 Now you want to print what the operator will do, so go ahead and type something like f"{x} and {y}" and this is going to equal… So here, go ahead and type what the actual and operator will do to the inputs x and y.

04:52 And so remember, x and y are going to be taking on the values of True and False generated by the product() function. Go ahead and run that. And you know what?

05:01 Before you do that, put in this tab (\t) just to make it a little bit nicer. When you print it, it’ll add a little bit more space. Go ahead and run it.

05:10 So, those are the four possible outputs to the and operator. The only time that the and operator returns True is when both operands are True, and otherwise it’s going to return False.

05:24 Let’s take a look at an example that demonstrates the short-circuiting feature of the and operator. Go ahead and define a function that we’ll call print_and_return(). It takes one input, say, x.

05:39 It’s going to print a simple statement that just says f"I am returning {x}". And then it’s just simply going to return the value x.

05:52 And let’s add a little bit of space before the "I", just so that when the print statement is returned, we get a little bit of space there. Okay.

06:02 Now let’s use this function with the and operator. Go ahead and type True and, the function, and let’s pass into the function the value of False.

06:17 So what’s going to happen here is that the and operator will first evaluate the first input, which is in this case True. Then it will pass on and take a look at the second expression, or the second input. It’s going to evaluate that, which is this function, and then it’s going to return the value returned by the function.

06:38 So, in this case, we have this side effect generated by the function that prints the statement, the function returns False, and so that means that the whole and operator returns False.

06:49 If we change this to True, then in this case the and operator will return True. Now, the way that you define this function, we can also pass in, say, 2/3.

07:05 And so Python will do that computation and return it. And if you did something like this, say 1/0, then of course you’re going to get a division error.

07:17 Let’s now try this in the case that the first input to the and operator is False. Go ahead and type False and, and then we’ll use the same function, and we’ll pass into the function the value of True.

07:30 And so what’s going to happen here is that the and operator evaluates the first input, the first input has a value of False, and so the and operator short-circuits. Notice that the side effect of the function, or the function itself, is never evaluated.

07:48 So it doesn’t matter what the second expression is because the first input is False, the and operator short-circuits and simply returns that value of False. That means that, for instance, if you were to actually write in here 1/0, that never returns a ZeroDivisionError because that function is never evaluated. All right, this ends this lesson on the and operator. In the next lesson, we’ll take a look at the or operator.

08:17 I’ll see you then.