Python Variables

Understanding Variables in Python

To create a variable in Python, you simply assign a value to a variable using the assignment operator '='. Here's a basic syntax for creating a variable:

variable_name = value

variable_name = value

• variable_name: The name you choose for your variable. It can be any valid identifier (letters, numbers, and underscores but cannot start with a number).
• value: The data you want to store in the variable (could be a string, number, or more complex data types).

Rules for Naming Variables in Python

In Python, valid variable names must adhere to a few rules:

1. Start with a letter or underscore _: Variable names must begin with a letter (a-z, A-Z) or an underscore _.
   • Valid: a, my_name, _age
   • Invalid: 123var, 1_name (Starts with a digit)
2. Contain only letters, digits, and underscores: After the first character, variable names can include letters (a-z, A-Z), digits (0-9), and underscores _.
   • Valid: my_var_123, value1, b_99
   • Invalid: my-var, score$ (Contains invalid characters like hyphen or dollar sign)
3. Case-sensitive: Variable names are case-sensitive, so Var and var would be considered two different variables.
   • Var, var, vAr are all valid but distinct
4. Length: There's no specific restriction on the length of variable names, but it's best to keep them meaningful and readable.
5. Reserved keywords cannot be used as variable names (e.g., for, if, while).
6. Here are some examples of valid variables:
   • name
   • _age
   • score_1
   • max_value
   • user_input
7. Examples of invalid variable names:
   • 1_name - Starts with a digit (invalid)
   • my-var - Contains a hyphen (invalid; only underscores are allowed)
   • score$ - Contains a special character (`$`) (invalid)
   • &result - Starts with an ampersand (&), which is not allowed
   • for - A reserved keyword in Python (invalid)
   • my variable - Contains a space (invalid; variable names can't have spaces)
   • class_name - Although this follows syntax rules, "class" is a reserved keyword, and using it as part of the variable name might confuse the reader (not technically invalid, but discouraged)

Best Practices for Naming Python Variables

When naming variables in Python, case sensitivity is important. The recommended case style for variables follows the snake case convention:

Snake Case (recommended naming convention)

• Description: This style uses all lowercase letters, with words separated by underscores '_'.
• Purpose: Snake case is the recommended style for variable names in Python, as outlined in PEP 8 (Python's style guide).
• Examples: my_variable_name, user_input_data, max_value

Example 1: Creating a simple variable

To create a variable in Python, you assign a value to a name. In this case, we're storing a value in a variable.

name = "john"
print(name)

name = "john"
print(name)

How It Works:

• name: This is the variable created to store the value "john".
• "John": This is a value (a message) that’s assigned to the variable name.
• When the code runs, Python assigns the value "John" to the variable name, and then it prints the value of name to the screen.

Output:

John

John

Example 2: Reassigning a variable's value

You can change the value of a variable at any time by simply assigning it a new value.

age = 25
age = 30
print(age)

age = 25
age = 30
print(age)

How It Works:

• age: This is the variable that initially holds the value 25.
• age = 30: The value of the variable age is changed to 30.
• When the code runs, it prints the most recently assigned value of age, which is 30.

Output:

30

30

Exercises

Try the following exercises to practice creating and using variables in Python:

# Exercise 1: Print your favorite color
# Replace 'color' with your favorite color.
color = "Blue"
print(color)

# Exercise 1: Print your favorite color
# Replace 'color' with your favorite color.
color = "Blue"
print(color)

# Exercise 2: Print your age
# Replace '21' with your actual age
age = 21
print(age)

# Exercise 2: Print your age
# Replace '21' with your actual age
age = 21
print(age)

# Exercise 3: Reassign a variable and print the result
# Replace '20' with any number or string
number = 20
print(number)

# Exercise 3: Reassign a variable and print the result
# Replace '20' with any number or string
number = 20
print(number)

*Tip: After completing an exercise, feel free to experiment with different data types (like strings, numbers, and more) to explore how variables work in Python!

Frequently Asked Questions

What's Next?

Next, you'll learn about data types in Python. Understanding the different types of data (like integers, floats, strings, etc.) will help you know how to store and manipulate information in your program.