Python Day-构造函数，继承，超载

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构造函数：

构造函数是一个唯一的函数，当创建一个类的对象时，它会自动调用。

- >创建时，它用于初始化它们。 ->构造方法命名为__init __（）

->用来表示当前对象

class employee:
    def __init__(self, name, qual,department, year):
        self.empname = name
        self.dept = department
        self.joining_year = year
        self.qual = qual

    def work(self):
        print("working", self.empname, self.dept, self.joining_year)

emp1 = employee("guru", "b.com", "development", 2025)
emp2 = employee("pritha", "m.e.,", "design", 2025)
emp1.work()

working guru development 2025

class employee:
    salary = 25000
    def __init__(self, name, qual,department, year):
        self.empname = name
        self.dept = department
        self.joining_year = year
        self.qual = qual

    def work(self):
        print("working", self.empname, self.dept, self.joining_year)
        print(self.salary)
emp1 = employee("guru", "b.com", "development", 2025)
emp2 = employee("pritha", "m.e.,", "design", 2025)
emp1.work()

working guru development 2025
25000

__ dict __：__dict__是一个将所有实例属性存储为词典的对象的特殊属性。>

class employee:
    salary = 25000
    def __init__(self, name, qual,department, year):
        self.empname = name
        self.dept = department
        self.joining_year = year
        self.qual = qual

    def work(self):
        print("working", self.empname, self.dept, self.joining_year)
        print(self.salary)
emp1 = employee("guru", "b.com", "development", 2025)
emp2 = employee("pritha", "m.e.,", "design", 2025)
print(employee.__dict__)
print(emp1.__dict__)
print(emp2.__dict__)

{'__module__': '__main__', 'salary': 25000, '__init__': , 'work': , '__dict__': , '__weakref__': , '__doc__': none}
{'empname': 'guru', 'dept': 'development', 'joining_year': 2025, 'qual': 'b.com'}
{'empname': 'pritha', 'dept': 'design', 'joining_year': 2025, 'qual': 'm.e.,'}

类方法是一种在类本身而不是实例上运行的方法。它是使用@classmethod装饰器定义的，并将cls（类参考）作为其第一个参数。

class employee:
    salary = 25000
    def __init__(self, name, qual,department, year):
        self.empname = name
        self.dept = department
        self.joining_year = year
        self.qual = qual

    @classmethod
    def credit_salary(cls):
        print("credit salary on last day of every month")

    def work(self):
        print("working", self.empname, self.dept, self.joining_year)
        print(self.salary)
emp1 = employee("guru", "b.com", "development", 2025)
emp2 = employee("pritha", "m.e.,", "design", 2025)
employee.credit_salary()

>输出：

嵌套类：

>嵌套类（内类）是在另一类中定义的类。

class college:
    def init(self):
        print("college constructor")

    class dept:
        def init(self):
            print("dept constructor")

        def work(self):
            print("working")

principal = college()
hod = principal.dept()
hod.work()

>示例：2（直接使用外部类名来调用内部类）

class college:
    def __init__(self):
        print("college constructor")

    class dept:
        def __init__(self):
            print("dept constructor")

        def work(self):
            print("working")

hod = college().dept()
hod.work()

output ：（两个示例的相同输出）

college constructor
dept constructor
working

构建器过载：

- >构造函数过载是指在类中定义具有不同参数集的多个构造函数。 -> python不支持多个构造函数（

方法）
-> python通过默认参数值和可变长度参数（*args或** kwargs）列表实现了过载。 >示例：

class supermarket:
    def __init__(self,product_name, price, *discount):
        self.product_name = product_name
        self.price = price
        self.discount = discount

    def buy(self):
        print(self.product_name, self.price, self.discount)class shapes:
    def find_area(self, side1, side2):
        print(side1 * side2)


class square(shapes):
    pass

s = square()
s.find_area(5,5)

class rectangle(shapes):
    pass
r = rectangle()
r.find_area(10,8)

product1 = supermarket("soap", 50, 10)
product2 = supermarket("brush", 60,20)
product1.buy()
product2.buy()
product3 = supermarket("rice", 60)
product3.buy()

soap 50 (10,)
brush 60 (20,)
rice 60 ()

- >继承使我们能够定义一个从另一类继承所有方法和属性的类。

- >

是所继承的类，也称为基类。

- >child class是从另一个类继承的类，也称为派生类。

> >单继承：一个子类从单亲类继承。

25
80

class father:
    def work(self):
        print("mechanical engineer")

class mother:
    def work(self):
        print("software engineer")

class child(mother, father):
    def work(self):
        print("business person")

child = child()
child.work()

print(100+200)
print("hi"+"hello")
print(100*3)
print("hi"*3)

300
hihello
300
hihihi

class book:
    def __init__(self, pages):
        self.pages = pages

    def __add__(self, second):
        print(self.pages, second.pages)
        return self.pages + second.pages

book1 = book(300)
book2 = book(200)
print(book1 + book2)

300 200
500

class Employee:
    def __init__(self, name, salary):
        self.name = name
        self.salary = salary

    def __mul__(self,other):
        return self.salary * other.days

class TimeSheet:
    def __init__(self, name, days):
        self.name = name
        self.days = days

emp1 = Employee("Guru", 1000)
timesheet1 = TimeSheet("Guru", 25)
print("Monthly salary:",emp1 * timesheet1)