Classes and methods

Defining classes and methods

class ClassName:
    def method_name(self, other_parameters):
        body_of_method

Special methods

• Special methods start and end with __.

• Special methods have specific names, like __init__ for the constructor or __str__ for the conversion to string.

• The methods __str__ and __repr__ allow you to define human-readable and unambiguous string representations of your objects, respectively.

• By defining methods like __eq__, __ne__, __lt__, __gt__, __le__, and __ge__, you can control how objects of your class are compared.

With the __init__ method:

用途：接受參數的傳入，並帶入變數 self.XXX

class Apple:
    def __init__(self, color, flavor):
        self.color = color
        self.flavor = flavor

honeycrisp = Apple("red", "sweet")
fuji = Apple("red", "tart")
print(honeycrisp.flavor)
print(fuji.flavor)

With the __str__ method:

When you print() something, Python calls the object’s __str__() method and outputs whatever that method returns

class Apple:
    def __init__(self, color, flavor):
        self.color = color
        self.flavor = flavor

    def __str__(self):
        return "an apple which is {} and {}".format(self.color, self.flavor)

honeycrisp = Apple("red", "sweet")
print(honeycrisp)

# prints "an apple which is red and sweet"

With the custom method

class Triangle:
    def __init__(self, base, height):
        self.base = base
        self.height = height
    def area(self):
        return 0.5 * self.base * self.height
    def __add__(self, other):
        return self.area() + other.area()
    
triangle1 = Triangle(10, 5)
triangle2 = Triangle(6, 8)
print("The area of triangle 1 is", triangle1.area())
print("The area of triangle 2 is", triangle2.area())
print("The area of both triangles is", triangle1 + triangle2)