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Python Variables

In Python, variables are used to store data that can be referenced and manipulated during program execution. A variable is essentially a name that is assigned to a value. Unlike many other programming languages, Python variables do not require explicit declaration of type. The type of the variable is inferred based on the value assigned.

Variables act as placeholders for data. They allow us to store and reuse values in our program.

1. What is a Variable?​

A variable is like a container for storing data values. You don’t need to declare its type explicitly — Python handles it dynamically.

x = 5
y = "Hello"

Here:

  • x is of type int
  • y is of type str

2. How to Declare and Assign Variables​

You simply write a variable name, use the assignment = operator, and assign a value.

a = 10
name = "GeeksForGeeks"
price = 99.99
is_active = True

Python automatically understands the type of variable.

3. Multiple Assignments in One Line​

Python allows assigning values to multiple variables in a single line.

x, y, z = 1, 2, 3

You can also assign same value to multiple variables:

a = b = c = 100

4. Variable Naming Rules​

  • Must start with a letter (a–z, A–Z) or an underscore (_)
  • Can contain letters, digits, and special character like underscore.
  • Are case-sensitive (name and Name are different).
  • Cannot use reserved keywords like if, class, def, etc.
# Valid
my_var = 1
_var = 2
var3 = 3

# Invalid
3var = 10       # starts with digit
my-var = 20     # hyphen not allowed
def = 30        # 'def' is a keyword

5. Standard Data Types in Python​

Python variables can hold different types of data:

data-type table

6. Type Checking with type()​

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

7. Changing Variable Type Dynamically​

Python allows dynamic typing:

x = 5
print(type(x))  # <class 'int'>

x = "Hello"
print(type(x))  # <class 'str'>

8. Deleting a Variable with del​

You can remove a variable from memory using del.

x = 100
del x

print(x)  # Raises NameError

9. Scope of Variables​

There are two scopes of variables:

10. Global Variable​

Declared outside functions, accessible anywhere.

x = "global"

def show():
    print(x)

show()  # Output: global

11. Local Variable​

Declared inside functions and accessible only inside them.

def greet():
    msg = "Hello"
    print(msg)

greet()
print(msg)  # Error: NameError

🟢 The global Keyword​

Use global to modify global variables inside a function.

x = 10

def update():
    global x
    x = 20

update()
print(x)  # Output: 20

12. Memory Management in Python​

  • Python variables are names bound to objects in memory.
  • Use id() to get the memory address (or reference ID) of a variable.
x = 5
print(id(x))

If two variables have the same immutable value, they may share the same memory.

a = 100
b = 100
print(id(a) == id(b))  # True

🟢 Example Program​

# Python Variable Example

name = "Dhruba"
age = 22
price = 49.99
is_valid = True
items = ["pen", "notebook"]

print("Name:", name)
print("Age:", age)
print("Price:", price)
print("Valid:", is_valid)
print("Items:", items)

Output:

Name: Dhruba
Age: 22
Price: 49.99
Valid: True
Items: ['pen', 'notebook']

Summary​

  • Python variables store different types of data without explicit declaration.
  • Variables are case-sensitive and follow naming rules.
  • Scope determines where a variable is accessible.
  • global and del are important keywords for variable handling.
  • Python handles memory management internally but allows inspection via id().

Highlights​

  • Covers both global and local variables
  • Explains del, global, and id() functions
  • Includes formatted tables and output blocks
  • Beginner-friendly explanation with examples