Object Oriented Programming

Introduction

This repository is a collection of Python knowledge that I have learned from various sources. The main purpose of this repository is to help me to remember the basic Python knowledge that I have learned.

1. Object Oriented Programming
2. Refactor Code
3. Design Patterns

Attributes

Attributes are the characteristics of an object. They are data stored inside a class or instance and represent the state or quality of the class or instance. In short, attributes store information about the instance.

Mutable vs Immutable

• Immutable Types: int, float, complex, bool, None, str, bytes, tuple, frozenset, mappingproxy
• Mutable Types: list, set, dict

Function and method arguments should not be mutable.

Details in object-oriented-programming/attribute_mutable_immutable.py file.

Class Variable vs Instance Variable

• Class Variable: Shared by all instances of the class (global variable)

class User
    first_name = 'Khoi'
    last_name = 'VN'

• Instance Variable: Unique to each instance (init method)

class User
    def __init__(self, first_name, last_name):
        self.first_name = first_name
        self.last_name = last_name

Details in object-oriented-programming/class_variable_instance_variable.py file.

Annotations

Annotations are used to provide type hints to functions and methods. They are not enforced by the interpreter, but they can be used by external tools such as linters, IDEs, and type checkers.

class User:
    first_name: str
    last_name: str

    def __init__(self, first_name: str, last_name: str) -> None:
        self.first_name = first_name
        self.last_name = last_name

Details in object-oriented-programming/class_variable_instance_variable.py file.

Slots

Slots are used to explicitly declare data members and deny the creation of __dict__ and __weakref__ (save memory). It is only available for new-style classes.

class User:
    __slots__ = ['first_name', 'last_name']

    def __init__(self, first_name: str, last_name: str) -> None:
        self.first_name = first_name
        self.last_name = last_name

Details in object-oriented-programming/attribute_slots.py file.

Property Decorator

Property is a special kind of attribute that computes its value when accessed. It is used to implement getters and setters.

class User:
    def __init__(self, first_name: str, last_name: str) -> None:
        self.first_name = first_name
        self.last_name = last_name

    @property
    def full_name(self) -> str:
        return f'{self.first_name} {self.last_name}'

    @full_name.setter
    def full_name(self, value: str) -> None:
        self.first_name, self.last_name = value.split(' ', 1)

Details in object-oriented-programming/property_decorator.py file.

Methods

Method Types

• Instance Method: It is bound to an instance of a class. It can access the instance through self.
• Static Method: It is bound to a class rather than its object. It does not require a class instance creation. It is not dependent on the state of the object.
• Class Method: It is bound to a class rather than its object. It can access the class through cls.

class User:
    def instance_method(self) -> None:
        return 'instance method'

    @staticmethod
    def static_method() -> None:
        return 'static method'

    @classmethod
    def class_method(cls) -> None:
        return 'class method'

Details in object-oriented-programming/method_in_class.py file.

Static Method

Static method is a method that is bound to a class rather than its object. It does not require a class instance creation. It is not dependent on the state of the object.

class User:
    def full_name_static_function(first_name: str, last_name: str) -> str:
        return f'{first_name} {last_name}'

    @staticmethod
    def full_name_static_method(first_name: str, last_name: str) -> str:
        return f'{first_name} {last_name}'

Details in object-oriented-programming/method_staticmethod.py file.

Class Method

Class method is a method that is bound to a class rather than its object. It can access the class through cls.

class User:
    def __init__(self, first_name: str, last_name: str) -> None:
        self.first_name = first_name
        self.last_name = last_name

    @classmethod
    def from_string(cls, name_string: str) -> User:
        first_name, last_name = name_string.split(' ', 1)
        return cls(first_name, last_name)

Details in object-oriented-programming/method_classmethod.py file.