Variables and Data Types in Python

🟢 Beginner

📖 Definition

In Python, a Variable is a named reference that points to an object in memory. Python is dynamically typed, meaning you do not need to declare variable data types explicitly—the Python interpreter automatically infers the data type at runtime based on the value assigned to it.

🇮🇳 Hindi

Python mein variables declare karte waqt datatype (int, str, etc.) nahi likhna padta. Python assignment ke aadhar par datatype khud determine kar leta hai. Datatype check karne ke liye type() function ka use hota hai.

🚩 Marathi

Python madhye variables saathi data type bolava lagat nahi (dynamic typing). Value kashi ahe tyavrun Python type tharavto. Type bghnyasathi type() vapara.

🤔 Why Do We Use Them?

Variables allow programs to store, reference, update, and manipulate dynamic data values—such as user inputs, shopping cart totals, API responses, and database records.

🧠 Simple Explanation

Think of a Python variable as a sticky name tag attached to a package in a warehouse. The name tag is the variable name (e.g., user_age), and the item inside the package is the object (e.g., 25). You can easily peel off the sticky tag and attach it to a different package later.

📝 1. Core Primitive Data Types

Python provides built-in primitive data types:

Data Type Category Description Example
int Integer Whole numbers (arbitrary precision) age = 25
float Floating Point Real numbers with decimals price = 999.50
bool Boolean Logical state (True or False) is_active = True
str Text String Sequence of Unicode characters name = "Rahul"
NoneType None Represents absence of a value result = None

📝 2. Type Checking & Type Casting

  • type(var): Returns the exact class type of an object.
  • isinstance(var, Type): Returns True if variable matches specified type.
  • Type Conversion: Explicitly converting values using int(), float(), str(), bool().
score_str = "95"
score_int = int(score_str)  # Converts string "95" to integer 95
price_float = float(100)    # Converts integer 100 to float 100.0

📝 3. Variable Naming Rules (snake_case)

  • Use snake_case for Python variable names (user_age, total_amount).
  • Names can contain letters, numbers, and underscores (_).
  • Names cannot start with a number.
  • Cannot use reserved Python keywords (if, class, def, import, for).

💡 Complete Example: Variables, Types & Conversion

# Product E-Commerce Summary
product_name = "Wireless Headphones"  # str
unit_price = 2499.00                 # float
quantity_str = "2"                   # str (from input)
in_stock = True                      # bool
discount_code = None                 # NoneType

# Type Conversion: Parsing quantity string to integer
quantity = int(quantity_str)
total_cost = unit_price * quantity

print("=== PRODUCT DETAILS ===")
print(f"Product Name : {product_name} (Type: {type(product_name).__name__})")
print(f"Unit Price   : ₹{unit_price} (Type: {type(unit_price).__name__})")
print(f"Quantity     : {quantity} (Type: {type(quantity).__name__})")
print(f"In Stock?    : {in_stock}")
print(f"Total Cost   : ₹{total_cost:.2f}")

# Checking Type with isinstance()
print(f"Is Total Cost a float? : {isinstance(total_cost, float)}")

👀 Output

=== PRODUCT DETAILS ===
Product Name : Wireless Headphones (Type: str)
Unit Price   : ₹2499.0 (Type: float)
Quantity     : 2 (Type: int)
In Stock?    : True
Total Cost   : ₹4998.00
Is Total Cost a float? : True

⚠️ Common Mistakes

  • Trying to perform string concatenation with integers directly ("Score: " + 95 causes TypeError; use f-string f"Score: {95}" or str(95)).
  • Confusing the equality operator == (compares values) with the identity operator is (compares memory object ID).
  • Using Python reserved words as variable names (e.g. naming a variable list or type).

🛡️ Safety / Important Notes

In Python, numbers (int, float), booleans, strings, and tuples are immutable (their values cannot be changed in-place; modified variables point to new objects in memory).

🌍 Real-World Usage

Data pipeline processing, handling REST API JSON responses, dynamic configuration settings, and data science dataframes.

🧪 Try It Yourself

  1. Declare a variable user_age = "24". Convert it to an integer, add 5 to it, and print f"Age in 5 years: {user_age + 5}".
  2. Check type(None) in your terminal REPL.

🎯 Mini Challenge

Write a program that declares a floating-point temperature in Fahrenheit temp_f = 98.6, converts it to Celsius using formula (temp_f - 32) * 5/9, and prints the result rounded to 1 decimal place.

🔗 Related Topics

🧭 Navigation

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