Python Variables – The Complete Beginner‘s Guide

Variables are a fundamental concept in Python programming. They allow you to store, manipulate, and reuse data throughout your code. Having a solid grasp of variables is essential for writing effective Python programs.

In this comprehensive beginner‘s guide, we‘ll dive deep into everything you need to know about Python variables. By the end, you‘ll understand what variables are, how to create and use them effectively, and some expert tips and best practices. Let‘s get started!

What are Variables in Python?

You can think of a variable as a container that holds a value. It‘s a way to give a name to a piece of data so you can reference and use it in different parts of your program.

For example, let‘s say you want to store a user‘s name in your program. You could create a variable called name and assign it a value:

name = "John"

Now, whenever you want to use the user‘s name in your program, you can simply refer to the name variable instead of retyping "John" each time.

Variables make your code more readable, reusable, and maintainable. Imagine if you had a program with hundreds of lines of code that used a user‘s name dozens of times. If you ever needed to change the name, you‘d have to find and replace it in each spot. With a variable, you only need to change the value once.

Python‘s popularity and widespread usage means variables are a concept you‘ll encounter frequently:

• Python is the most popular programming language according to the TIOBE Index as of 2023
• It‘s used by tech giants like Google, Netflix, Dropbox, and Spotify
• Python is the fastest-growing major programming language according to Stack Overflow insights

So as you learn Python, understanding variables is crucial.

Creating Variables in Python

Creating a variable in Python is a simple, two-step process:

1. Choose a name for your variable
2. Assign the variable a value using the = operator

For example:

message = "Hello World!"
num_users = 50

In the first line, we create a variable named message and assign it the string value "Hello World!". In the second line, we create a variable named num_users and assign it the integer value 50.

One important thing to note is that Python is a dynamically-typed language. This means you don‘t need to specify the type of value a variable will hold ahead of time. The Python interpreter infers the type based on the value you assign.

So in our examples above, message is inferred to be a string because we assigned it a string value, while num_users is inferred to be an integer because we assigned it an integer value.

This dynamic typing is one of Python‘s conveniences compared to statically-typed languages like Java or C++. It allows for quicker and more flexible development.

Naming Variables

While you can choose almost any name you want for your variables, there are some rules and best practices to keep in mind:

• Variable names can only contain letters, numbers, and underscores. They cannot contain spaces or special characters.
• Variable names must start with a letter or underscore, not a number.
• Variable names are case-sensitive. So myVariable and myvariable would be two different variables.
• Avoid using Python keywords like if, for, while, def, class, etc. as variable names.

In addition to these rules, there are some conventions that most Python programmers follow:

• Use descriptive names for variables. A name like user_count is better than c.
• Use lowercase letters for most variables.
• Separate words with underscores. This is known as snake_case.
• Use capital letters for constants that don‘t change like PI = 3.14159.

Here are some examples of valid and invalid variable names:

# Valid variable names
count = 10
user_name = "John"
_private_var = "secret"

# Invalid variable names 
5count = 10     # starts with a number
user name = "John"   # contains a space
import = "module"    # Python keyword

Following these naming guidelines will make your code more readable and maintainable, especially as your programs grow larger.

Variable Types

As we mentioned earlier, Python has several built-in data types that variables can hold. Here are the most common ones:

Type	Example	Description
int	x = 5	Whole numbers (positive or negative)
float	price = 9.99	Numbers with decimal points
str	name = "Alice"	Text (in quotes)
bool	is_valid = True	True or False values
list	items = [1, 2, 3]	Ordered, mutable collection
tuple	point = (3, 4)	Ordered, immutable collection
dict	user = {"name": "Bob"}	Key-value pairs

You can use the type() function to check the type of a variable:

x = 10
print(type(x))   # <class ‘int‘>

message = "hello"  
print(type(message))  # <class ‘str‘>

is_valid = True
print(type(is_valid))  # <class ‘bool‘>

Knowing the type of your variables is important because different types support different operations and methods.

For example, you can use + to concatenate strings or add numbers, but not to combine a string and a number:

name = "Alice"
age = 30

print(name + " is " + age + " years old")  
# TypeError: can only concatenate str (not "int") to str

To fix this, you‘d need to convert age to a string first:

print(name + " is " + str(age) + " years old")
# "Alice is 30 years old"

Variable Scope

The scope of a variable refers to where in your program the variable is accessible. Python has two main scopes:

• Global scope: Variables defined outside any function. They can be accessed anywhere in your program.
• Local scope: Variables defined inside a function. They can only be accessed within that function.

For example:

# Global variable
message = "hello"

def greet():
    # Local variable 
    name = "John"
    print(message + " " + name)

greet()  # "hello John"
print(name)  # NameError: name ‘name‘ is not defined

In this example, message is a global variable. It can be accessed inside the greet() function. On the other hand, name is a local variable. It can only be accessed inside greet(). Trying to access it outside the function raises an error.

If you want to modify a global variable inside a function, you need to use the global keyword:

count = 0

def increment():
    global count
    count += 1

increment() 
print(count)  # 1

However, using global variables excessively can make your code harder to understand and maintain. It‘s generally better to use local variables and pass values as arguments to functions when needed.

Best Practices

Here are some tips to keep in mind when working with variables in Python:

• Use descriptive names for your variables. This makes your code more readable and self-documenting. For example, total_revenue is better than tr.

• Be consistent with your naming style. If you use snake_case, use it throughout your program. Don‘t mix styles like camelCase and PascalCase.

• Use constants for values that don‘t change. Constants are usually defined at the top of a file and use all capital letters with underscores:

MAX_CONNECTIONS = 100
API_KEY = "abc123"

• Avoid using single-letter variable names unless it‘s a conventional use like x, y, z for coordinates or i for a loop counter.

• Don‘t overwrite built-in Python functions or types with your own variables. For example, don‘t name a variable list or str.

• Initialize variables with a default value when it makes sense. This can prevent errors from accessing uninitialized variables:

count = 0
results = []
user = None

• Use type hints to specify expected variable types. Type hints are optional but can make your code more readable and help catch potential bugs:

def greet(name: str) -> str:
    return f"Hello {name}"

• Avoid using too many global variables. They can make your code harder to reason about and maintain. Instead, try to encapsulate related data into classes or pass data as arguments to functions.

• Use meaningful variable names, even for temporary variables. Names like temp or var don‘t convey much meaning.

• Don‘t be afraid to rename variables if you think of a better name later on. Most code editors have a rename feature that will update all references to the variable.

Conclusion

Variables are a core concept in Python programming. They allow you to store, reference, and manipulate data throughout your program.

In this comprehensive guide, we‘ve covered everything a beginner needs to know about Python variables:

• What variables are and why they‘re important
• How to create and assign values to variables
• Rules and conventions for naming variables
• Different data types variables can hold
• Variable scope – global vs local
• Tips and best practices from expert Python developers

Understanding variables is an essential step in your Python programming journey. As you continue to learn and build projects, you‘ll use variables constantly to work with all kinds of data.

Remember to give your variables meaningful names, be mindful of their types and scope, and follow best practices like using constants and type hints. With practice, using variables will become second nature.

Further Learning

If you want to dive even deeper into Python variables and related concepts, here are some great resources:

• Python Variables Tutorial from W3Schools
• Python Variables and Types from Real Python
• Python Variable Scope: Understanding LEGB from Real Python
• Official Python Documentation on Data Types
• PEP 8 – Style Guide for Python Code

Remember, the best way to solidify your understanding of variables is through practice. As you write more Python code and encounter different use cases, you‘ll gain an intuitive sense of when and how to use variables effectively.

Happy coding!

The content of this article is accurate as of August 2021 and is based on Python 3.x. Python and its usage are constantly evolving, so always refer to the official Python documentation for the most up-to-date information.