Python 3 Booleans - Logical Operators

Python 3: From Scratch to Intermediate BEGINNER LEVEL: Python 3 - Numbers and Booleans
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Transcript

As a short definition, we can say that the boolean data type defines only two possible values true and false. The name comes from George Boole, he was a 19th century English mathematician and philosopher. Now living history of sight and returning to Python, you can think of these two values as being equivalent to one and zero. In Python, true is written with a capital T and false with a capital F. So, keep that in mind. We have already seen true and false in some examples during the previous lecture. So they are not completely new to you at this point in the course.

Basically, they are used to evaluate whether an expression is true or false, and can be further used in conditional or loop structures, as we will see later in the course. For now, let's evaluate some basic expressions and see how Python evaluates each of them. So let's start with one equals eight. Calls one, which is true one equals equals two, which is false. Let's say the string Python equals equals Python. So we are comparing two strings.

Which is true. What if we compare Python with Python with a capital P, this time, we have to separate strings. So the result is false. Three is less than or equal to four, which is true, of course. Okay, so you get the idea. This was some pretty basic evaluations that we did.

Now, there are three main Boolean operations, each of them having a specific operator, the first operator is and the second operator is or, and the third operator is not. Let's analyze each of them and see how they work. And means that both operands should be true in order to have the entire expression evaluated as true. So let's see this in practice. Let's do an end operation between two true expressions. So let's say one equals equals one, and two equals equals true.

By the way, you can skip the parentheses, I'm just using them for better readability. And I advise you to do the same when dealing with longer expressions. So both expressions being evaluated as true, the final result is, of course true. Next, when performing an end operation between true false expressions, the result will be false. So let's try this. Let's say we have one equals equals two, and three equals equals two, with the end operator in between them, and the result is false.

The third case is when one expression is evaluated as true, and the other one is evaluated as false. This will also return false when using and so let's test this. Let's say that the first expression is a true expression and the second one is a false expression. So true and false will result in false the condition And here is that when using the end operator, if both expressions are true, then the result will also be true. On the other hand, if at least one expression is evaluated as false, then the result will be false as well. Now let's start with the OR operator, or works like this.

If at least one of the expressions is evaluated as true, then the final result is true. If they are both false, then the final result will be false as well. So when using or It is enough if only one expression is true, in order to have true as the final result. Let's see this in practice. So one equals equals one, or two equals equals two. The final result is true because both expressions are true.

Now what about one equals equals one, or two equals equals three. This expression is also evaluated as true because we have the OR operator in between a true expression and a false expression. Finally, let's make both expressions false So one equals equals true or true equals equals three, and that returns false. Finally, using the NOT operator means simply denying an expression. If that expression is true, then denying it will result in false right, and vice versa. Of course, let's try this.

So not one equals equals one, this results in false because we are negating a true expression. Consequently, not one equals equals two will result in true because we are negating a false expression. Okay, one more thing to keep in mind here, some Python values always evaluate to false. They are non 00 point 00 j, which means a complex number, the empty string, the empty list, the empty topple, the empty dictionary and so on. On the other hand, any values that are not equal to these values right here. So if we have for example, one or 2.5 or a string hello, they are evaluated as true.

And let's test this because Python provides the bool function to help us evaluate values and expressions as true or false. So let's use this function to check the always false values. Let's say bool. of non is false ball of zero, also ball of an empty string. Okay. And as I've said, all other values in Python are considered to be true.

So let's say ball of one ball of 2.2. Ball for an empty list, and we will talk more about lists very soon returns false. However, bool for a list that is not empty, let's say with a single element will return true, Boolean and logical operators are very useful in Python, especially when dealing with if Elif conditionals and while loops but more on that later.

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