Pythonic OOP pt. 1

This is a talk about some object-oriented programming characteristics in Python language.

Transcript

1. Pythonic OOP pt. 1 Caio Carrara 1
2. Disclaimer 2 This is far from an extensive approach of OOP or OOP in Python. Both because time and knowledge limitation :|
3. Why? 3
4. How? • OOP: quick intro • Defining objects • Magic (special) methods ◦ Protocols • Objects everywhere • Instance and class attributes • Class methods • Extra: mixins considerations 4
5. Object-oriented programming 5
6. From Alan Kay - pioneer in OOP “I thought of objects being like biological cells and/or individual computers on a network, only able to communicate with messages (...) OOP to me means only messaging, local retention and protection and hiding of state-process” https://userpage.fu-berlin.de/~ram/pub/pub_jf47ht81Ht/doc_kay_oop_en 6
7. Python official HOW TO “Objects are little capsules containing some internal state along with a collection of method calls that let you modify this state, and programs consist of making the right set of state changes.” https://docs.python.org/3/howto/functional.html 7
8. Defining objects 8
9. Defining objects 9
10. Defining objects 10
11. Defining objects 11
12. Defining objects 12
13. Defining objects 13
14. Defining objects 14
15. Defining objects 15
16. Defining objects 16
17. Defining objects 17
18. *-* Magic methods *-* 18
19. Python special method names (magic, dunder) 19 • Methods with special names: double underscore before and after the method name itself: ◦ __new__, __init__, __len__, __del__, __repr__, __str__ … • When writing Python code we shouldn’t call special methods explicitly. Python interpreter does that
20. Python special method names (magic, dunder) 20
21. Python special method names (magic, dunder) 21
22. Python special method names (magic, dunder) 22 https://docs.python.org/3/reference/datamodel.html#special-method-names
23. Magic methods: protocols 23
24. Python typing 24 • Dynamic typing: Python variable values has a type only on runtime. The variable values have a type and not the variable itself. • Strongly typed: Python restricts how the different types can interact with each other • Duck typing: “if it walks like a duck and it quacks like a duck, then it must be a duck”
25. Python special method names (magic, dunder) 25 • How is it possible to create a Collections-like object? ◦ Inheriting? ◦ Implementing an Interface? ◦ Making it “quack” (behave) like a Collection
26. Python special method names (magic, dunder) 26 • How is it possible to create a Collections-like object? ◦ Inheriting? ◦ Implementing an Interface? ◦ Making it “quack” (behave) like a Collection: following a protocol
27. Python special method names (magic, dunder) 27
28. Python special method names (magic, dunder) 28
29. Objects everywhere 29
30. Objects everywhere... https://docs.python.org/3/reference/datamodel.html 30
31. Objects everywhere... https://docs.python.org/3/library/functions.html#type 31
32. Objects everywhere... 32
33. Objects everywhere... 33
34. Objects everywhere... 34
35. Objects everywhere... 35
36. Instance and class attributes 36
37. Instance and class attributes 37
38. Instance and class attributes 38
39. Class methods 39 https://caiocarrara.com.br/blog/python-classmethod-o-que-e-e-quando-usar.html (PT-BR)
40. Class methods 40
41. Class methods 41
42. Class methods 42
43. Class methods - when to use them? • In Python everything is an object • Objects have state and behavior • Since Classes are objects as well, class methods should be used when it’s needed to extend a class object behavior 43
44. Class methods - when to use them? “Classes are callable. These objects normally act as factories for new instances of themselves, but variations are possible for class types that override __new__(). The arguments of the call are passed to __new__() and, in the typical case, to __init__() to initialize the new instance.” 44 https://docs.python.org/3/reference/datamodel.html
45. Class methods - when to use them? “Classes are callable. These objects normally act as factories for new instances of themselves, but variations are possible for class types that override __new__(). The arguments of the call are passed to __new__() and, in the typical case, to __init__() to initialize the new instance.” 45 https://docs.python.org/3/reference/datamodel.html
46. Class methods - when to use them? • Therefore we could consider the class methods as an way to extend the responsibility of a class object to create new instances of themselves 46
47. Class methods 47
48. Extra: mixins considerations 48
49. Mixins considerations 49 • The name was inspired by Steve's Ice Cream Parlor • The owner of the ice cream shop offered a basic flavor of ice cream (vanilla, chocolate, etc) and blended in a combination of extra items (nuts, cookies, fudge, etc.) and called the item a "mix-in" https://en.wikipedia.org/wiki/Mixin
50. Mixins considerations 50 • Mixins are not the place to implement business logic • Mixins being used by only one class is a code smell • Ideally someone could remove without too much pain the mixin dependency without breaking the core functionality of an object (loose coupling) • Mixins are never directly instantiated
51. Mixins considerations: anti-pattern 51
52. Mixins considerations: Django example 52
53. Mixins considerations: Django example 53
54. Thanks! Questions? 54