Variables in Python

A variable is a name that refers to a value stored in the computer’s memory. In Python, variables are used to store data that can be used and manipulated later in the program.

Key Points About Variables in Python

1. No explicit declaration needed: You don’t need to declare a variable type beforehand. Just assign a value, and Python figures out the type automatically.

2. Dynamic typing: The type of a variable can change during execution.

3. Case sensitive: myVar and myvar are different variables.

4. Naming rules:

   • Variable names must start with a letter (a-z, A-Z) or underscore _.
   • The rest can be letters, digits (0-9), or underscores.
   • Cannot use Python reserved keywords like if, for, while, etc.

Assigning Variables

Assign a value using the = operator:

x = 10           # Integer
name = "Alice"   # String
pi = 3.14        # Float
is_valid = True  # Boolean

Variables Can Change Type

var = 5          # Initially an integer
print(var)       # Output: 5

var = "Hello"    # Now a string
print(var)       # Output: Hello

Multiple Assignments

You can assign values to multiple variables in one line:

a, b, c = 1, 2, 3
print(a, b, c)  # Output: 1 2 3

Assign the same value to multiple variables:

x = y = z = 0
print(x, y, z)  # Output: 0 0 0

Using Variables

You can use variables in expressions:

a = 10
b = 20
c = a + b
print(c)  # Output: 30

Variable Types (Examples)

age = 25               # int
price = 19.99          # float
first_name = "John"    # str
is_student = False     # bool

Variable Naming Best Practices

• Use descriptive names, e.g., total_price, user_age.
• Use lowercase with underscores for readability (snake_case).
• Avoid single letters except for counters or indices (i, j).

Example Program Using Variables

# Store user information
name = "Alice"
age = 30
height = 5.5  # in feet

print(f"{name} is {age} years old and {height} feet tall.")

Output:

Alice is 30 years old and 5.5 feet tall.