Python Variable Full Guide

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✅ Python Variables – Full Guide

🔹 What is a Variable?

A variable is a container for storing data values. It acts as a label pointing to a memory location where the value is stored.

📌 Think of it like:

age = 25
Means “store 25 in a box labeled age.”

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🔹 How to Create a Variable

name = "Arvind"
age = 25
price = 99.99
is_online = True

✅ Python detects the data type automatically — no need to declare type like in C++ or Java.

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🔹 Variable Naming Rules

Rule	Example
Must start with a letter or _	✅ name, _score
Can't start with a number	❌ 1age
No spaces	❌ user name
Case-sensitive	Name ≠ name
Use descriptive names	✅ user_age

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🔹 Data Types with Variables

# Integer
x = 10

# Float
pi = 3.14

# String
city = "Nashik"

# Boolean
logged_in = False

Use type() to check data type:

print(type(city))  # <class 'str'>

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🔹 Multiple Assignments

a, b, c = 1, 2, 3
x = y = z = 100

print(a, b, c)
print(x, y, z)

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🔹 Dynamic Typing

Python is dynamically typed, so you can reassign different data types to the same variable.

x = 10        # int
x = "Ten"     # now it's a string

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🔹 Type Casting (Convert Data Type)

a = "123"
b = int(a)  # converts string to integer

x = 5.5
y = str(x)  # converts float to string

print(type(b), type(y))

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🔹 Constants in Python (by convention)

Python doesn't have real constants, but we use uppercase to show it shouldn’t change.

PI = 3.14159
GRAVITY = 9.8

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🔹 Memory Reference (Advanced Insight)

a = 5
b = a  # both point to same memory

print(id(a), id(b))  # Same IDs

Reassigning b = 6 will change its memory location.

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✅ Best Practices

✅ Use snake_case for variable names
✅ Make names meaningful
✅ Use constants for fixed values
✅ Don’t reuse variables unnecessarily
✅ Keep naming consistent

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🔚 Summary

Concept	Example
Create Variable	x = 5
Data Types	int, float, str, bool
Check Type	type(x)
Reassign Variable	x = "hello"
Multiple Assignment	a, b = 1, 2

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