简明Python教程学习笔记7

11、面向对象的编程

（1）简介

　　略

（2）self

　　假如你有一个类称为MyClass和这个类的一个实例MyObject。

　　当你调用这个对象的方法MyObject.method(arg1, arg2)的时候，

　　这会由Python自动转为MyClass.method(MyObject, arg1, arg2)——这就是self的原理了。

（3）类

　　略

（4）对象的方法

　　略

（5）__init__方法

　　略

（6）类与对象的变量

　　类的变量 由一个类的所有对象（实例）共享使用。只有一个类变量的拷贝，所以当某个对象对类的变量做了改动的时候，这个改动会反映到所有其他的实例上。

　　对象的变量 由类的每个对象/实例拥有。因此每个对象有自己对这个域的一份拷贝，即它们不是共享的，在同一个类的不同实例中，虽然对象的变量有相同的名称，但是是互不相关的。

# coding=utf-8
class Person(object):
    """Represents a person."""
    population = 0  # 类变量

    def __init__(self, name):
        """Initializes the person's data."""
        self.name = name  # 实例变量
        print "(Initializing %s)" % self.name

        # When this person is created, he/she
        # adds to the population
        Person.population += 1

    def __del__(self):
        """I am dying."""
        print "%s says bye." % self.name

        Person.population -= 1

        if Person.population == 0:
            print "I am the last one."
        else:
            print "There are still %d people left." % Person.population

    def say_hi(self):
        """Greeting by the person.
        
        Really, that's all it does."""
        print "Hi, my name is %s." % self.name

    def how_many(self):
        """Prints the current population."""
        if Person.population == 1:
            print "I am the only person here."
        else:
            print "We havve %d persons here." % Person.population


if __name__ == "__main__":
    print "*" * 20 + "Swaroop Begin" + "*" * 20
    swaroop = Person("Swaroop")
    swaroop.say_hi()
    swaroop.how_many()

    print "*" * 20 + "Kalam Begin" + "*" * 20
    kalam = Person("Abdul Kalam")
    kalam.say_hi()
    kalam.how_many()

    print "*" * 20 + "say_hi && how_many" + "*" * 20
    swaroop.say_hi()
    swaroop.how_many()

    print "*" * 20 + "End" + "*" * 20

输出：

（7）继承

# -*- coding:utf-8 -*-


class SchoolMember(object):
    """Represents any school member."""

    def __init__(self, name, age):
        self.name = name
        self.age = age
        print "(Initialized SchoolMember:%s)" % self.name

    def tell(self):
        """Tell my details."""
        print "Name:\"%s\" Age:\"%s\"" % (self.name, self.age)


class Teacher(SchoolMember):
    """Represents a teacher."""

    def __init__(self, name, age, salary):
        SchoolMember.__init__(self, name, age)  # 调用父类的初始化
        self.salary = salary
        print "(Initialized Teacher:%s" % self.name

    def tell(self):
        SchoolMember.tell(self)  # 通过类调用父类的方法，不需要创建对象
        print "Salary:\"%d\"" % self.salary


class Student(SchoolMember):
    """Represents a student."""

    def __init__(self, name, age, marks):
        SchoolMember.__init__(self, name, age)
        self.marks = marks
        print "(Initialized Student:%s)" % self.name

    def tell(self):
        SchoolMember.tell(self)
        print "Marks:\"%d\"" % self.marks


if __name__ == "__main__":
    print "**" * 20 + "Teacher" + "**" * 20
    t = Teacher("Mrs.Shrividya", 40, 30000)

    print "**" * 20 + "Student" + "**" * 20
    s = Student("Swaroop", 22, 75)

    print "**" * 44
    members = [t, s]
    for member in members:
        member.tell()

输出：