Work with variables in Python

Previously, we compared data types to the categories we have for different ingredients we use when cooking, like vegetables or meat.
Some of these categories we use for data types are the string, float, integer, Boolean, and list.
Now, let's make another comparison.
When working in the kitchen, we also use storage containers.
These containers can hold a lot of different things.
After one meal, a container might hold rice, and after another, it could hold something different, like pasta.
In a similar way, in Python, we have variables.
A variable is a container that stores data.
To create a variable, you need a name for it.
Then, you add an equals sign and then an object to store in it.
Creating a variable is often called assignment.
The best practice for naming variables is to make the names relevant to what they're being used for.
Let's use a variable to store a device ID.
We'll name our variable device_ID, add the equals sign, and then assign it a value of h32rb17.
Because the data type for this variable is a string, we'll place that value in quotation marks.
Let's run the code.
Our variable is now saved into Python.
The purpose of creating variables is to use them later in the code.
Using variables can also be referred to as "calling" them.
To call a variable, you type its name.
This tells Python to use the object that the variable contains.
Let's add to the code we've just written and call a variable.
Let's just have it print the variable.
To do this, we use the print function and ask it to print the value stored in the device ID variable.
When using a variable in our print function, we don't use quotation marks.
This time, when we run it, something happens.
Python prints h32rb17 to the screen.
Let's add one more line of code to demonstrate the difference between printing a variable and printing a string.
We'll ask Python to print a string that contains another device ID: m50pi31.
Because this is string data and not a variable, we place it in quotation marks.
Now, let's run the code and see the results.
It executes both print statements.
The first reads the variable and prints the value it contains: h32rb17.
And the second reads the specified string and prints m50pi31.
But if we could use the string directly, why do we need variables?
Well, we often use variables to simplify our code or make it cleaner and easier to read.
Or if we needed a very long string or number, storing it in a variable would let us use it throughout our code without typing it all out.
In the previous example, the variable stored string data, but variables can store a variety of data types.
Variables have the data type of the object currently storing them.
If you're unsure about the data type stored inside of a variable, you can use the type function.
The type function is a function that returns the data type of its input.
Let's use the type function in Python.
We'll start by creating our variable.
Then, we'll add a line of code that includes the type function.
This line asks Python to tell us the data type of the device ID variable and to assign this to a new variable called data_type.
After this, we can print the data_type variable to the screen.
Perfect!
Python tells us that the value that device ID contains a string.
When working with variables, it's important to keep track of their data types.
If you don't, you could get a type error.
A type error is an error that results from using the wrong data type.
For example, if you try to add a number and a string, you will get a type error because Python cannot combine those two data types together.
It can only add two strings or two numbers.
Let's demonstrate a type error.
First, we'll reuse our device ID variable that stores a string value.
Then, we'll define another variable called number and assign an integer value to it.
Let's add a print statement that outputs the sum of these variables, and then we'll run this.
We ended up with an error because we cannot add a string to a number.
Let's cover one more topic related to variables.
Earlier, we mentioned how variables are like containers.
What they hold can change.
After we define a variable, we can always change the object inside of it.
This is called reassignment.
Reassigning a variable is very similar to assigning it in the first place.
Let's try this out and reassign a variable.
We'll start by assigning the same string of h32rb17 to our variable device_ID.
We will also include a line of code to print this variable.
Now, let's try reassigning the variable.
We type this variable's name, add an equals sign, and then add the new object.
In this case, we'll use the string n73ab07 as the new device ID.
We'll also ask Python to print the variable again.
Let's see what happens when we run this.
Python prints two lines of output.
The first print statement came before reassignment, so it first prints the string of h32rb17.
But the second print statement came after it changed.
That's why the second output to the screen is the string n73ab07.
With this code, we reassigned a variable with a string value to another string value, but it's also possible to reassign a variable to a value of another data type.
For instance, we can reassign a variable with a string value to an integer value.
Variables are an essential part of Python, and as we progress through this course, you'll become more familiar with them.