Python: Variables and Basic Data Types

Variables are the one of the fundamental building blocks of Python that are used to hold data in memory.

Variables have two components, name and type. The data in the variables can be referenced by their names. Type defines what type of data it stores.

Let's start by creating one.

Declaration

Declaring a variable is incredibly simple in Python. Unlike in other programming languages, you do not need to specify the type of variable, it is done automatically for you.

Example of variable declaration looks like this:

name = "John Doe"
x = 777
print(name)
print(x)

The above code block prints

John Doe
777

• A variable is declared and assigned a value using the assignment operator =
  
• Python treats bool as a special type of integer. Technically, True has a value of 1 and False has a value of 0.
  
• A string is a collection of zero or more characters. Strings are commonly declared using single quotation marks, but you can also use double quotation marks.
  
• Python treats integer numbers and decimal numbers differently.

Variable Naming Rules

Here are the rules for what are valid Python variable names:

• The variable name must begin with a letter or underscore
• The variable name cannot begin with a number or symbol
• Throughout the entire variable name, it can only contain alpha-numeric characters with the only exception being underscores

With that in mind, here are some examples of valid Python variable names:

apples
_apples
_apples_

And here are examples of invalid Python variable names:

1apples
app les
$apples
%apples

Data Types

Python supports five standard data types. We've already seen two of them already, Numbers and String. Here is the entire list:

• Numbers
• String
• List
• Tuple
• Dictionary

It is useful to know that you can get the type of a variable by using the type method, like so:

name = "John Doe"
print(type(name))
print(name)

pi = 3.1415926
print(type(pi))
print(pi)

x = 777
print(type(x))
print(x)

isSuccess = True
print(type(isSuccess))
print(isSuccess)

Output of the code prints:

<class 'str'>
John Doe
<class 'float'>
3.1415926
<class 'int'>
777
<class 'bool'>
True

We'll get into lists, tuples, and dictionaries in later lessons.