In this Python tutorial, we take a deep dive into @classmethod, one of the most powerful features of object-oriented programming in Python.
🔍 We explore:
What class methods are and how they differ from instance methods
Why we use cls instead of self
How to create alternative constructors like from_string()
The use of named constructors (like Pizza.margherita())
Managing and tracking class-level state using @classmethod
✅ And most importantly — how to correctly track subclass data like user counts!
🚨 In this lesson, we also fix a common mistake: using User._user_count += 1 inside __init__, which causes all subclasses (like AdminUser) to increment the wrong counter. Learn how self.__class__._user_count += 1 gives you subclass-aware tracking.
💡 By the end, you'll have a solid understanding of:
When to use class methods
How they help write cleaner, more extensible code
How Python's class hierarchy affects class variables
👨💻 CODE EXAMPLES INCLUDED throughout — so you can follow along and test it out live!
🔗 Timestamps
0:00 - What is a class method?
0:17 - Alternative constructors (from_string)
4:31 - Named constructors (Pizza.margherita)
6:21 - Tracking users with class variables
9:17 - Why subclass counts break
9:18 - ✅ Fixing it with self.__class__._user_count
9:30 - Summary and best practices
SOURCE CODE :
Alternative constructor (1st example) : https://github.com/bhumikapandey1992/...
Named Constructor (2nd example) : https://github.com/bhumikapandey1992/...
Managing class level state (3rd example) :
https://github.com/bhumikapandey1992/...
Recommended books :
1) https://amzn.to/4o4TxmP
2) https://amzn.to/46Q8XoA
3) https://amzn.to/3IDPTjq
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