Python编程_Lesson015_类的基础用法

和其它高级语言一样，Python也有类将数据和函数有效的组合起来。

类的定义

class UserInfo(object):    passtype(UserInfo)<class 'type'>type(UserInfo)<class 'type'>type(list)<class 'type'>

这样我们就定义了一个空类，查看它的类型也是class，和其它的list、dict等类型一样。

给类对象绑定属性

class UserInfo(object):    passuser_info = UserInfo()user_info.name = "root"user_info.name'root'user_info.password = "root"user_info.password'root'

我们成功的给user_info这个对象绑定了username和password两个属性。
但是我们绑定的这两个属性只存在于user_info这个对象，它们并不属于UserInfo()这个类，我们来检验一下

class UserInfo(object):    passuser_info = UserInfo()user_info.name = "root"user_info.name'root'user_info.password = "root"user_info.password'root'user_info2 = UserInfo()user_info2.usernameTraceback (most recent call last):  File "<input>", line 1, in <module>AttributeError: 'UserInfo' object has no attribute 'username'user_info2.passwordTraceback (most recent call last):  File "<input>", line 1, in <module>AttributeError: 'UserInfo' object has no attribute 'password'

我们可以看到user_info2这个对象并没有username和password这两个属性。
看到这里，我们就会这样想，有没有办法让这个UserInfo类在定义的时候就有一些属性呢？答案是肯定的。

类属性的绑定

我们使用基类的__init__()函数进行类属性的绑定，它相当于其它高级编程语言的构造函数，从这里看应该是初始化函数。

class UserInfo(object):    def __init__(self, username, password, salary, balance):        self.username = username        self.password = password        self.salary = salary        self.balance = balanceuser_info_1 = UserInfo("root", "root", 3000, 2000)user_info_1.username'root'user_info_1.username'root'user_info_1.salary3000user_info_1.balance2000

这样我们就成功的给UserInfo这个类绑定了username、password、salary和balance这四个属性并且可以访问了。
需要注意的是：__init__函数的第一个参数无论如何都是self，否则是无法进行绑定的，因为不知道绑定到哪里！！！在生成对象的时候，必须要传递四个参数，否则也是生成不成功的！！！
虽然这样能够对类属性进行一个一个的输出，但是我们能不能让这个类自己输出所有的属性的，也是可以的。

类方法和属性的绑定（类属性是共有的）

为了方便，我们改成pycharm IDE来进行编写！

class UserInfo(object):    def __init__(self, username, password, salary, balance):        self.username = username        self.password = password        self.salary = salary        self.balance = balance    def print(self):        print("User Name:%s Password:%s Salary:%d Balance:%d" %(self.username, self.password, self.salary, self.balance))def main():    user_info_1 = UserInfo("root", "root", 3000, 1600)    user_info_1.print()    user_info_1.salary = 10    user_info_1.print()if __name__ == "__main__":    main()

打印结果如下：

User Name:root Password:root Salary:3000 Balance:1600User Name:root Password:root Salary:10 Balance:1600

从结果上我们会发现一个问题，我们的月工资竟然被随随便便的更改了！！！
可不可以不被更改呢？
当然也是可以的！！！将类属性变为私有即可，但是这种方法也不是绝对的，因为在Python中没有绝对的私有属性。

类方法和属性的绑定（类属性是共有的）

class UserInfo(object):    def __init__(self, username, password, salary, balance):        self.__username = username        self.__password = password        self.__salary = salary        self.__balance = balance    def print(self):        print("User Name:%s Password:%s Salary:%d Balance:%d"              % (self.__username, self.__password, self.__salary, self.__balance))def main():    user_info_1 = UserInfo("root", "root", 3000, 1600)    user_info_1.print()    user_info_1.salary = 10    user_info_1.print()if __name__ == "__main__":    main()

打印结果如下：

User Name:root Password:root Salary:3000 Balance:1600User Name:root Password:root Salary:3000 Balance:1600

这次没有被修改。但是我们也没有办法访问某一个属性和修改某一个属性了，那又该如何呢？？？
我们可以使用setter和getter解决。

如下所示：

class UserInfo(object):    def __init__(self, username, password, salary, balance):        self.__username = username        self.__password = password        self.__salary = salary        self.__balance = balance    def get_username(self):        return self.__username    def get_password(self):        return self.__password    def get_salary(self):        return self.__salary    def get_balance(self):        return self.__balance    def set_username(self, username):        self.__username = username    def set_password(self, password):        self.__password = password    def set_salary(self, salary):        self.__salary = salary    def set_balance(self, balance):        self.__balance = balance    def print(self):        print("User Name:%s Password:%s Salary:%d Balance:%d"              % (self.__username, self.__password, self.__salary, self.__balance))def main():    user_info_1 = UserInfo("root", "root", 3000, 1600)    user_info_1.print()    user_info_1.set_username("admin")    print(user_info_1.get_username())    user_info_1.print()if __name__ == "__main__":    main()

结果如下：

User Name:root Password:root Salary:3000 Balance:1600adminUser Name:admin Password:root Salary:3000 Balance:1600

成功的设置和访问了某一个属性。

我们还可以在设置属性的时候加上一些判断条件，满足条件，则可以修改，否则修改失败！

例如：
在设置之前，需要输入管理员密码，如果输入成功，则可以修改，否则将不能修改。

class UserInfo(object):    def __init__(self, username, password, salary, balance):        self.__username = username        self.__password = password        self.__salary = salary        self.__balance = balance    def get_username(self):        return self.__username    def get_password(self):        return self.__password    def get_salary(self):        return self.__salary    def get_balance(self):        return self.__balance    def set_username(self, username):        set_status = True        if input("Please input the super administrator password:") == "123456":            self.__username = username        else:            set_status = False        return set_status    def set_password(self, password):        set_status = True        if input("Please input the super administrator password:") == "123456":            self.__password = password        else:            set_status = False        return set_status    def set_salary(self, salary):        set_status = True        if input("Please input the super administrator password:") == "123456":            self.__salary = salary        else:            set_status = False        return set_status    def set_balance(self, balance):        set_status = True        if input("Please input the super administrator password:") == "123456":            self.__balance = balance        else:            set_status = False        return set_status    def print(self):        print("User Name:%s Password:%s Salary:%d Balance:%d"              % (self.__username, self.__password, self.__salary, self.__balance))def main():    user_info_1 = UserInfo("root", "root", 3000, 1600)    user_info_1.print()    if user_info_1.set_username("admin"):        print("set success!")    else:        print("set failed!")    print(user_info_1.get_username())    user_info_1.print()if __name__ == "__main__":    main()

结果如下

User Name:root Password:root Salary:3000 Balance:1600Please input the super administrator password:123set failed!rootUser Name:root Password:root Salary:3000 Balance:1600

类中的权限控制

Python类中的权限控制是非常弱的，尽管我们在属性前面加上了两个下划线，但是我们依然可以修改这个属性，请看下面的例子：

class UserInfo(object):    def __init__(self, username, password, salary, balance):        self.__username = username        self.__password = password        self.__salary = salary        self.__balance = balance    def get_username(self):        return self.__username    def get_password(self):        return self.__password    def get_salary(self):        return self.__salary    def get_balance(self):        return self.__balance    def set_username(self, username):        set_status = True        if input("Please input the super administrator password:") == "123456":            self.__username = username        else:            set_status = False        return set_status    def set_password(self, password):        set_status = True        if input("Please input the super administrator password:") == "123456":            self.__password = password        else:            set_status = False        return set_status    def set_salary(self, salary):        set_status = True        if input("Please input the super administrator password:") == "123456":            self.__salary = salary        else:            set_status = False        return set_status    def set_balance(self, balance):        set_status = True        if input("Please input the super administrator password:") == "123456":            self.__balance = balance        else:            set_status = False        return set_status    def print(self):        print("User Name:%s Password:%s Salary:%d Balance:%d"              % (self.__username, self.__password, self.__salary, self.__balance))def main():    user_info_1 = UserInfo("root", "root", 3000, 1600)    user_info_1.print()    user_info_1._UserInfo__username = "admin"    user_info_1.print()if __name__ == "__main__":    main()

结果如下：

User Name:root Password:root Salary:3000 Balance:1600User Name:admin Password:root Salary:3000 Balance:1600

我们竟然这样修改了username的值，这充分说明Python中没有绝对的访问权限控制！

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Python中的继承关系

class Animal(object):    def eat(self):        print("Animal eat...")class Pig(Animal):    passclass Dog(Animal):    passdef main():    aa = Pig()    aa.eat()    bb = Dog()    bb.eat()if __name__ == "__main__":    main()

打印结果：

Animal eat...Animal eat...

从结果可以看出，Pig类和Dog类都继承了父类Animal的eat方法，当然我们还可以对父类中的方法进行重写。
例如：

class Animal(object):    def eat(self):        print("Animal eat...")class Pig(Animal):    def eat(self):        print("Pig eat...")class Dog(Animal):    passdef main():    pig = Pig()    pig.eat()    dog = Dog()    dog.eat()if __name__ == "__main__":    main()

打印结果如下：

Pig eat...Animal eat...

Pig类重写的eat方法被成功重写了！！！

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基类object中的函数

在object类中有很多前面有两个下划线的函数，它们都具有一定的意义，比如：

‘_init_()’函数

‘init()’函数表示类在初始化的时候会被调用。

‘_len_()’函数

该函数是在调用len函数求可迭代对象的元素个数时候会被调用

class UserInfo(object):    def __init__(self, username, password, salary, balance):        self.__username = username        self.__password = password        self.__salary = salary        self.__balance = balance    def get_username(self):        return self.__username    def get_password(self):        return self.__password    def get_salary(self):        return self.__salary    def get_balance(self):        return self.__balance    def set_username(self, username):        set_status = True        if input("Please input the super administrator password:") == "123456":            self.__username = username        else:            set_status = False        return set_status    def set_password(self, password):        set_status = True        if input("Please input the super administrator password:") == "123456":            self.__password = password        else:            set_status = False        return set_status    def set_salary(self, salary):        set_status = True        if input("Please input the super administrator password:") == "123456":            self.__salary = salary        else:            set_status = False        return set_status    def set_balance(self, balance):        set_status = True        if input("Please input the super administrator password:") == "123456":            self.__balance = balance        else:            set_status = False        return set_status    def __len__(self):        print("len() is called!")        return 0    def print(self):        print("User Name:%s Password:%s Salary:%d Balance:%d"              % (self.__username, self.__password, self.__salary, self.__balance))def main():    user_info_1 = UserInfo("root", "root", 3000, 1600)    len(user_info_1)if __name__ == "__main__":    main()

结果如下：

len() is called!0

剩下的比如‘__abs__()’函数、‘__and__()’函数、‘__or__()’函数等等都也是这样的用法！！！