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# 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.

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