Local Variables

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From the course by Rice University

Python Programming Essentials

485 оценки

Rice University

Python Programming Essentials

485 оценки

Course 1 of 4 in the Specialization Introduction to Scripting in Python

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.

From the lesson

Functions

This module will teach you how to define and call functions. Functions allow you to write code once that you can execute repeatedly with different inputs.

What is a Function?6:48

Calling Functions6:59

Defining Functions11:28

Local Variables4:55

Meet the Instructors

Scott Rixner
Professor
Computer Science
Joe Warren
Professor
Computer Science

[MUSIC]

Now we want to talk about local variables.

What is a local variable?

Well, it's a variable that's created inside of a function.

These local variables only exist for the duration of the execution of

the particular function call in which they were created.

They don't exist outside of the function call, and

they are not the same variables when you call the function again.

Doesn't quite make sense?

Well, let's take a look at how all this works.

So let's take a look at a function that converts Fahrenheit to Celsius.

There're two different kinds of local variables.

The first is the parameters of the function.

So you can see here we have a parameter called fahrenheit,

that is going to be one type of local variable inside of these function.

The other are variables that are created inside the function itself, so

you can see offset, multiplier celsius.

These variables are completely local to this function as well.

And what this effectively means is that when you call this function,

there becomes a new variable called farenheit,

a new variable called offset multiplier and celsius right.

And when the function ends, these variables go away all right.

They don't exist any longer, all right.

And then the next time you call the function a new set get created, all right.

So in general this doesn't sort of affect things,

functions work the way that we've shown you so far, okay.

I set up the temperature, I called Fahrenheit to Celsius.

And let's print out the values, okay.

I converted 95 to Celsius, which is 35, all right, and we can see that here.

Now inside the function what's going on?

Inside the function we have variables called fahrenheit,

offset, multiplier, and celsius, and

you can see their values right before we return from the function here.

Fahrenheit is 95, offset is 32, okay, the multiplier

is 0.555, and celsius is 35.0.

All right, when we return, okay, those variables all go away.

They don't exist anymore, but

we still have variables called temperature and converted, which we can print out.

All right, notice that converted is the variable that we assigned

the result of the function two.

We're not using the name celsius which was inside of the function,

even though that is what was returned, we return celsius.

We're returning the value that celsius was naming, and that value was 35.

That value then got assigned to converted,we can now

use it as converted outside, but we can't use it as celsius outside.

Okay, now that all is straightforward, and is what I've shown you before.

But let's look at something a little bit more sort of demonstrative here.

Okay, now I'm going to create variables before I call the function,

that had the same names as these variables inside the function.

So you can see here, I have fahrenheit, offset, multiplier, and celsius, and

I have intentionally assigned them all values that are different

than what they're going to take on inside the function, all right?

I'm going to print those values out before.

I'm going to call the function, all right?

And then I'm going to print them out afterwards, and you're going to see that

they're completely unaffected by this function called even though variables have

exactly the same name, are being created and used inside the function.

Okay so let's look at this all right.

So look at the before and after lines first.

Notice they are completely unchanged, 27 to 19 and 77.

Look inside the function,

the variables with exactly the same names, have completely different values now.

Because they were local to the function while the function is executing

variables with those names get created that are completely different

than the variables with those names outside of the function, all right.

They take on their values, the function returns, those values go completely away,

we don't have them anymore, they're gone, all right?

So when we print them out outside of the function,

we're getting the variables that existed outside the function that still exist

at the time that we call this print all right, okay.

The result is as expected we converted 32 degrees farenheit to celsius we

expected 0, we got 0, and that's what new temp needle was assigned to okay.

It's important to remember that the parameters of a function and

the variables that are created inside a function are local to that function.

They only exist during the execution of one particular function call.

Every time you call the function,

a new set of these local variables get created and used right.

And then when the function in it returns, those variables go away.

Outside of the function, even if variables are named the same okay,

they're actually different variables, right.

This can be a little bit confusing at first, but

you'll get the hang of it pretty quickly.

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