Python Variable

What is a Variable in Python?

A variable in Python is a named container that stores a value. You can think of it as a label for a memory location.

Creating Variables in Python

Python uses dynamic typing, which means you don’t need to declare the data type of a variable explicitly.

Syntax:

variable_name = value

Example:

x = 5
name = "Alice"
pi = 3.14
print(x)      # 5
print(name)   # Alice
print(pi)     # 3.14

Output:

5
Alice
3.14

Variable Naming Rules

Reassigning Variables

You can change the value and type of a variable at any time.

x = 10
x = "Now I’m a string"
print(x)

Output:

Now I’m a string

Multiple Assignments

Python allows multiple assignments in one line.

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

x = y = z = 100
print(x, y, z)   # 100 100 100

Output:

1 2 3
100 100 100

Best Practices for Using Variables

Bad vs Good Examples

# Bad
a = 100
b = 0.3

# Good
discount_rate = 100
tax_rate = 0.3

Quick Recap

What Are Data Types in Python?

In Python, data types define the kind of value a variable can hold. Python is dynamically typed, meaning you don't have to declare the type explicitly — Python infers it at runtime.

Categories of Python Data Types

1. Numeric Types

a) int – Whole numbers

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

Output:

<class 'int'>

b) float – Decimal numbers

pi = 3.14
print(type(pi))  # <class 'float'>

Output:

<class 'float'>

c) complex – Complex numbers

z = 2 + 3j
print(type(z))  # <class 'complex'>

Output:

<class 'complex'>

2. Text Type

a) str – Strings (sequence of Unicode characters)

name = "Python"
print(type(name))  # <class 'str'>

Output:

<class 'str'>

3. Sequence Types

a) list – Ordered, mutable, allows duplicates

fruits = ["apple", "banana", "cherry"]
print(type(fruits))  # <class 'list'>

Output:

<class 'list'>

b) tuple – Ordered, immutable, allows duplicates

coordinates = (10.5, 20.5)
print(type(coordinates))  # <class 'tuple'>

Output:

<class 'tuple'>

c) range – Immutable sequence of numbers

r = range(5)
print(list(r))  # [0, 1, 2, 3, 4]

Output:

[0, 1, 2, 3, 4]

4. Mapping Type

a) dict – Key-value pairs, unordered (as of Python 3.7+, insertion ordered)

person = {"name": "Alice", "age": 25}
print(type(person))  # <class 'dict'>

Output:

<class 'dict'>

5. Set Types

a) set – Unordered, no duplicates

numbers = {1, 2, 2, 3}
print(numbers)  # {1, 2, 3}

Output:

{1, 2, 3}

b) frozenset – Immutable set

frozen = frozenset([1, 2, 3])
print(type(frozen))  # <class 'frozenset'>

Output:

<class 'frozenset'>

6. Boolean Type

a) bool – True or False

is_active = True
print(type(is_active))  # <class 'bool'>

Output:

<class 'bool'>

7. Binary Types

a) bytes

b = b"hello"
print(type(b))  # <class 'bytes'>

Output:

<class 'bytes'>

b) bytearray

ba = bytearray(5)
print(ba)  # bytearray(b'\x00\x00\x00\x00\x00')

Output:

bytearray(b'\x00\x00\x00\x00\x00')

c) memoryview

mv = memoryview(bytes(5))
print(type(mv))  # <class 'memoryview'>

Output:

<class 'memoryview'>

Best Practices for Working with Data Types