[Python] class __init__(self) 基本概念

1. 需宣告時給予初始化值

class Student:

    def __init__(self, id, name):
        self.id = id
        self.name = name

if __name__ == '__main__':
    s = Student(1, 'george')
    print(s.id, s.name)

2. 直接賦予值

class Student:

    def __init__(self):
        self.id = 2
        self.name = 'george'
        self.sex = 'boy'

if __name__ == '__main__':
    s = Student()
    s2 = Student()

    print(s.id, s.name, s.sex)
    print(s2.id, s2.name, s2.sex)

3. (常見使用方式) 如果有填寫就給予初始值，若無，則賦予值。

class Student:

    def __init__(self, id=1, name='george', sex='boy'):
        self.id = id
        self.name = name
        self.sex = sex

if __name__ == '__main__':
    s = Student(1, 'Peter')
    s2 = Student(2, 'kate', 'girl')

    print(s.id, s.name, s.sex)
    print(s2.id, s2.name, s2.sex)

4. (接續3) 也可使用空值後，後續再添加屬性。

class Student:

    def __init__(self, id=1, name='george', sex='boy'):
        self.id = id
        self.name = name
        self.sex = sex
        self.score = {}

if __name__ == '__main__':
    s = Student(1, 'Peter')
    s2 = Student(2, 'kate', 'girl')

    s.height = 160
    s.weight = 60
    s.score['english'] = 90
    s.score['music'] = 85

    print(s.id, s.name, s.sex, s.score)
    print(s2.id, s2.name, s2.sex, s2.score)

5. 其他? (可將屬性不放在__init__()裡面，或是之後再自行增加屬性也可)

class Student:
    height = 180
    weight = 79

    def __init__(self, id=1, name='george', sex='boy'):
        self.id = id
        self.name = name
        self.sex = sex

if __name__ == '__main__':
    s = Student(1, 'Peter')
    s2 = Student(2, 'kate', 'girl')

    s.height = 160
    s.weight = 60

    print(s.id, s.name, s.sex, s.height, s.weight)
    print(s2.id, s2.name, s2.sex, s2.height, s2.weight)

如果屬性不放在__init__()裡面，且函數又要使用屬性時呢?

class Student:
    height = 1.78
    weight = 80

    def __init__(self, id=1, name='george', sex='boy'):
        self.id = id
        self.name = name
        self.sex = sex
        self.score = {}

    def cal_BMI(self, height, weight):
        bmi = weight / pow(height, 2)
        return bmi

if __name__ == '__main__':
    s = Student(1, 'Peter')
    s2 = Student(2, 'kate', 'girl')

    s.height = 1.60
    s.weight = 60
    s.score['english'] = 90
    s.score['music'] = 85
    bmi = s.cal_BMI(s.height, s.weight)

    print(s.id, s.name, s.sex, s.score, bmi)
    print(s2.id, s2.name, s2.sex, s2.score)

參考資料：

定義類別

關於Python的類別(Class)...基本篇

Python3 教學 #05 (Ch9: Class: 繼承、建構子、多型、封裝、覆載)

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