This course will introduce you to the wonderful world of Python programming! We'll learn about the essential elements of programming and how to construct basic Python programs. We will cover expressions, variables, functions, logic, and conditionals, which are foundational concepts in computer programming. We will also teach you how to use Python modules, which enable you to benefit from the vast array of functionality that is already a part of the Python language. These concepts and skills will help you to begin to think like a computer programmer and to understand how to go about writing Python programs. By the end of the course, you will be able to write short Python programs that are able to accomplish real, practical tasks. This course is the foundation for building expertise in Python programming. As the first course in a specialization, it provides the necessary building blocks for you to succeed at learning to write more complex Python programs. This course uses Python 3. While many Python programs continue to use Python 2, Python 3 is the future of the Python programming language. This first course will use a Python 3 version of the CodeSkulptor development environment, which is specifically designed to help beginning programmers learn quickly. CodeSkulptor runs within any modern web browser and does not require you to install any software, allowing you to start writing and running small programs immediately. In the later courses in this specialization, we will help you to move to more sophisticated desktop development environments.
Logical Expressions
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Do curso por Rice University
Python Programming Essentials
534 ratings
Na lição
Logic and Conditionals
This module will teach you how to use logic and conditionals to change the behavior of the program based upon values within the program.
Conheça os instrutores
Scott RixnerProfessor
Computer Science
Joe WarrenProfessor
Computer Science
Boolean logic is a fundamental part of programming,
so we are going to have to write boolean logical expressions in our programs.
We've shown you how to do this mathematically,
but now it's time to figure out how to do it in Python.
Here's a simple program that demonstrates how to write logical expressions in Python.
All right, first we have to actually understand how to write the booleans true and false.
And in Python, hey this is pretty easy.
It's just the words true and false,
but you have to capitalize them.
Okay, so, as you can see here,
I've assigned True to value1 and False to the variable value2.
Okay, so, true and false are just boolean values.
You can use them just like we use numbers in the past.
Okay, and you can assign them to variables and
then the variables will hold those boolean values.
You can see here, when we run this,
Python prints out the words True and False for
us because value1 and value2 hold those values of True and False.
These are not strings though.
These are actual boolean values,
so I can do logical operations on them.
So, let's start with NOT, okay.
Let's do the boolean NOT here. We see that.
Okay? As expected, when I use NOT on value1,
which was originally True, I get False.
And NOT value2, which was originally False, I get true.
Okay, so you can see that Python uses the English language word for the NOT operation.
Let's look at logical AND.
Okay, again, Python uses the English language word here,
AND to be logical AND,
so I'm going to do value1 and value1.
So that should be True and True,
which should that evaluate too?
You knew it's True, right?
Okay. Let's see what happens.
Yes, we get true there.
All of the others 2 are False.
Why? Because value2 is False.
And when you do logical AND with one False value,
you always get False.
All right? Moving on.
Let's look at logical OR.
Yet again, Python uses the English language word
OR to represent the logical OR operation.
And when we do this we're going to get True, True, False.
Okay, value1 was True so when I have value1 OR'd with anything else,
either itself or value2, we get True.
Value2 OR'd with value2.
They're both False. Okay, we get False. All right? Makes sense.
Now, I can't stress enough that it's very
nice that Python uses English language words here.
Right? It's very easy to see what's going on in your program.
You have the words True and False to represent the boolean values.
We have the English words NOT,
AND and OR to represent the Boolean operations.
OK? And so, when you look at the program it's fairly straightforward what's going on.
Now, so far these have all been
simple boolean expressions with only one boolean operator, okay?
Just like with arithmetic we can also have
compound expressions with multiple boolean operators.
So let's take a look at that.
All right, I added two new values,
value3 and value4, made them both True and now I have
a more complex compound boolean expression here.
And we run it and it evaluates to True.
A couple of things. First, you should try this yourself.
Okay, you should plug in the values of value 1, 2,
3 and 4 into that expression,
evaluate it yourself and see what you get.
Okay, check on Python, make sure Python knows what it is doing. All right?
You also want to make sure that you know what you're doing.
Okay, that you can understand how this gets
evaluated and how it evaluates to True. All right, the second thing.
We also have to worry about operator precedence here,
just like we did with arithmetic expressions.
Okay, these do not all have the same precedence.
If you go back to the Python documentation and look for operator precedence,
you will find the boolean logical operators on
that table and you'll find that NOT has a higher precedence than AND,
and AND has a higher precedence than OR.
So, if we just write an expression,
it might not evaluate in the way that you expect it to.
So, just as I recommended with arithmetic expressions,
I also recommend strongly here that you
always use parentheses in your boolean expressions.
Okay, so you'll see that I use parentheses here because I
wanted to change the way in which this was evaluated.
And so, make sure that you put parentheses so that it gets
evaluated in exactly the way that you want it to be.
So, now we've seen how we can write boolean logical expressions in Python.
Hopefully, you found it to be relatively straightforward.
Right? The fact that Python uses the English language words true, false,
not, and and or,
makes it pretty easy to both read and write these expressions.
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