Practical Python Design Patterns

Any production application requires good use of design patterns and this talk will be about popular design patterns/choices and their implementation. The talk will also cover basics of metaclasses and be using metaclasses in some design choices practically.

Transcript

1. PRACTICAL PYTHON DESIGN PATTERNS Ramanathan R Zentropy Technologies
2. About me ▪ Co-Founder/Director of Zentropy Technologies – We do end to end implementations of Fin Tech and Data science projects ▪ Before finding Zentropy, had a working experience of 10 years in a leading Hedge fund ▪ Part of the organizing team of PyCon India, 2018
3. Disclaimer J ▪ This presentation is based on Python 3 and later ▪ Almost all of this works in Python 2 as well – However, not really tested by Presenter ▪ Tit-bits gained over a period by working in Python.
4. What are classes in Python?
5. Classes in Python ▪ First class supported entities ▪ Technically class is an instance of type ▪ Sugar over the native ‘type’ in Python
6. What is type in Python?
7. type.__doc__ Init signature: type(self, /, *args, **kwargs) Docstring: type(object_or_name, bases, dict) Usages: 1. type(object) -> the object's type 2. type(name, bases, dict) -> a new type Type: type
8. Create a class using a type type(name, bases, dict) ▪ name – Name of the Class ▪ bases – Base classes of the class ▪ dict – The initial set of attributes and methods
9. Lifecycle of a class magic methods Instance requested __new__() call __init__() call Instance returned
10. Quick Recap ▪ Class is an instance of ’type’ – the holy grail ▪ Type can be used to create dynamic classes ▪ Life cycle of a class creation – It applies for the Class creation (instance of type).
11. What can I do with ‘type’?
12. Meta Classes ▪ A subclass of ‘type’ ▪ Change the way the class behaves ▪ Commonly called ‘Black magic’ in Python – Use it only when actually needed
13. The gory details of syntax ▪ Creating a Meta class class MyMetaClass(type): pass ▪ Using a Meta class class MyClass(metaclass=MyMetaClass): pass
14. The big picture type class Meta class (child of type) instance
15. Lifecycle of Meta class based class __new__() __init__() __call__() Meta class __new__() __init__() __call__() Actual class __new__() __init__() Actual class creation __call__() __new__() __init__() Class instance creation
16. The broad idea ▪ Class Behavior changes – – Use __new__() and __init__() of meta class ▪ Change Behavior of instance of the class (typical object) – Use __call__() of meta class
17. The Actual Patterns – Finally
18. Pattern 1 : Abstract classes
19. Pattern 2 : Abstract family of singleton classes
20. The Requirement ABC / Interface Singleton 1 Singleton 2 Singleton 3
21. Pattern 3 : Hashable Objects
22. Pattern 4 : Comparable Objects
23. Pattern 5 : Object Pools
24. Pattern 5 : Object Pools
25. Pattern 6 : Logging using Metaclasses
26. Pattern 7 : Sealed Classes
27. References ▪ Python 3 Meta Programming by David Beazley - https://www.youtube.com/watch?v=sPiWg5jSoZI ▪ Practical Metaclasses and Descriptors by Sim Zacks - - https://www.youtube.com/watch?v=Nay7lRPwnC4 ▪ Stack Overflow
28. Questions?
29. PyCon India, 2018 ▪ October 5-9, 2018 @ Hyderabad, India ▪ Tenth Anniversary ▪ CFP and Tickets open ▪ Keynote speakers – Carol Willing – Travis Oliphant – Armin Ronacher ▪ More details @ in.pycon.org