基于Python2.7.12的类学习。

1 使用class定义类

#!/usr/bin/env python
# coding=utf-8

class Person():
    def __init__(self, name):
        self.name = name 


if __name__ == '__main__':
    hunter = Person('JohnTian')
    print('The name of hunter:%s' %  hunter.name)

• __init__Python中的特殊函数名，用于根据类的定义创建实例对象，例如hunter

  __init__ 并不是必需的，只有当需要区分由该类创建的不同对象时，才需要指定__init__方法。

• self参数指向这个在被创建的对象本身，例如hunter

2 继承、覆盖和添加方法

继承从已有类中衍生出新的类，添加或修改部分功能。修改得到的新方法会覆盖原有的方法。我们习惯将原始的类称为父类、超类或基类，将新的类称作孩子类、子类或衍生类。

2.1 继承

class Car():
    def exclaim(self):
        print("I'm a car!")

class Yugo(Car):
    pass

baseCar = Car()
yugoCar = Yugo()
baseCar.exclaim()
yugoCar.exclaim()

2.2 覆盖方法

• 覆盖一般方法

class Car():
    def exclaim(self):
        print("I'm a car!")

class Bwm(Car):
    def exclaim(self):
        print("I'm a bwm car!")

baseCar = Car()
bwmCar = Bwm()
baseCar.exclaim()
bwmCar.exclaim()

• 覆盖__init__方法

class Person():
    def __init__(self, name):
        self.name = name 

class MDPerson(Person):
    def __init__(self, name):
        self.name = "Doctor " + name 

class JDPerson(Person):
    def __init__(self, name):
        self.name = name + ", Esquire"

person = Person('jt')
doctor = MDPerson('jt')
lawyer = JDPerson('jt')
print person.name
print doctor.name
print lawyer.name 

2.3 添加方法

class Car():
    def exclaim(self):
        print("I'm a car!")


class Yugo(Car):
    def exclaim(self):
        print "I'm a Yugo! Much like a Car, but more Yugo-ish."

    def need_a_fish(self):
        print "A little help here?"

yugoCar = Yugo()
yugoCar.need_a_fish()

3 使用super从父类获取帮助

class Person(object):
    def __init__(self, name):
        self.name = name


class EmailPerson(Person):
    def __init__(self, name, email):
        super(EmailPerson, self).__init__(name)
        # self.name = name
        self.email = email
bob = EmailPerson('bob', 'bob@gmail.com')
print bob.name
print bob.email

4 类属性的访问和设置

• 方法一(无修饰符)

class Duck(object):
    """docstring for Duck"""
    def __init__(self, input_name):
        super(Duck, self).__init__()
        self.__name = input_name

    def get_name(self):
        print 'inside the getter'
        return self.__name

    def set_name(self, input_name):
        print 'inside the setter'
        self.__name = input_name

    name = property(get_name, set_name)

fowl = Duck('Howard')
print fowl.name
print fowl.get_name()
fowl.name = 'johntian'
print fowl.name
fowl.set_name('jt')
print fowl.name

• 方法二(有修饰符)

class Duck(object):
    """docstring for Duck"""
    def __init__(self, input_name):
        super(Duck, self).__init__()
        self.__name = input_name

    @property
    def name(self):
        print 'inside the getter'
        return self.__name

    @name.setter
    def name(self, input_name):
        print 'inside the setter'
        self.__name = input_name

fowl = Duck('Howard')
print fowl.name
# print fowl.get_name()
fowl.name = 'johntian'
print fowl.name
# print fowl.__name # 无法在外部访问__name特性
print fowl._Duck__name  # 可以在外部访问_Duck__name特性

如果没有指定某一特性的setter属性(name.setter)，那么将无法从类的外部对它的值进行设置。

5 方法的类型

5.1 实例方法

self作为实例方法的第一个参数。

5.2 类方法

cls作为类方法的第一个参数。

5.3 静态方法

由@staticmethod装饰的方法。

class A(object):
    """docstring for A"""
    count = 0

    def __init__(self):
        super(A, self).__init__()
        A.count += 1

    def exclaim(self):
        print "I'm an A!"

    @classmethod
    def kids(cls):
        print "A has", cls.count, "little objects."


class CoyoteWeapon():
    @staticmethod
    def commercial():
        print "This CoyoteWeapon has been brought to you by Acme."
easy_a = A()
breezy_a = A()
wheezy_a = A()
A.kids() # A has 3 little objects.

6 鸭子类型

Python采用鸭子类型实现多态。

class Quote():
    def __init__(self, person, words):
        self.person = person
        self.words = words

    def who(self):
        return self.person

    def says(self):
        return self.words + '.'


class QuestionQuote(Quote):
    def says(self):
        return self.words + '?'


class ExclamationQuote(Quote):
    def says(self):
        return self.words + '!'


class BabblingBrook():
    def who(self):
        return 'Brook'

    def says(self):
        return 'Babble'


def who_says(obj):
    print obj.who(), 'says', obj.says()

hunter = Quote("John tian", "I'm hunting wabbits")
print hunter.who(), 'says:', hunter.says() # John tian says: I'm hunting wabbits.

hunter1 = QuestionQuote("Bugs Bunny", "What's up, doc")
print hunter1.who(), 'says:', hunter1.says() # Bugs Bunny says: What's up, doc?

hunter2 = ExclamationQuote("Daffy Duck", "It's rabbit season")
print hunter2.who(), 'says:', hunter2.says() # Daffy Duck says: It's rabbit season!

who_says(hunter)  # John tian says I'm hunting wabbits.
who_says(hunter1) # Bugs Bunny says What's up, doc?
who_says(hunter2) # Daffy Duck says It's rabbit season!
brook = BabblingBrook()
who_says(brook)   # Brook says Babble

7 特殊方法(魔术方法)

Python中的魔术方法名称以__开头和结束。

__init__: 它根据类的定义以及传入的参数对新创建对象进行初始化。

• 和比较相关的魔术方法

方法名称	使用
__eq__(self, other)	self == other
__ne__(self, other)	self != other
__lt__(self, other)	self < other
__gt__(self, other)	self > other
__le__(self, other)	self <= other
__ge__(self, other)	self >= other

• 和数学相关的魔术方法

方法名称	使用
__add__(self, other)	self + other
__sub__(self, other)	self - other
__mul__(self, other)	self * other
__floordiv__(self, other)	self // other
__truediv__(self, other)	self / other
__mod__(self, other)	self % other
__pow__(self, other)	self ** other

• 其他种类的魔术方法

方法名称	使用
__str__(self)	str(self)
__repr__(self)	repr(self)
__len__(self)	len(self)

__str__: 用于定义如何打印信息
__repr__: 交互式解释器输出变量

• 测试

class Word():
    def __init__(self, text):
        self.text = text

    def __eq__(self, word2):
        return self.text.lower() == word2.text.lower()

    def __str__(self):
        return self.text

    def __repr__(self):
        return 'Word("' + self.text + '")'

first = Word('ha')
second = Word('HA')
third = Word('eh')
print first == second
print first == third
# first
print first

8 组合(聚合)

继承子类和父类之间的关系是is-a的关系，实际操作中，子类对象还需要has-a关系。
例如：一只鸭子(子类)是鸟(父类)的一种(is-a)，它有一条尾巴(has-a)。

class Bill():
    def __init__(self, description):
        self.description = description


class Tail():
    def __init__(self, length):
        self.length = length


class DuckA():
    def __init__(self, bill, tail):
        self.bill = bill
        self.tail = tail

    def about(self):
        print 'This ducka has a ' + self.bill.description + ' bill and a ' + \
            self.tail.length + ' tail.'


tail = Tail('long')
bill = Bill('wide orange')
ducka = DuckA(bill, tail)
ducka.about() # This ducka has a wide orange bill and a long tail.

9 何时使用类和对象而不是模块

• 
  
• 当需要许多具有相似行为(方法)，但不同状态(特性属性)的实例时，使用对象是最好的选择。
• 类支持继承，模块不支持。
• 如果想要保证模块的唯一性，使用模块是最好的选择。
• 如果有一系列包含多个值的变量，并且它们能作为参数传入不同的函数，那么最好将它们封装到类里面。
• 用最简单的方式解决问题。
  

使用字典、列表和元组往往要比使用模块更加简单、简洁且快速，使用类则更复杂。

10 命名元组

命名元组是元组的子类，你既可以通过名称(.name)来访问其中的值，也可以通过位置进行访问([offset])。

使用nametuple函数来创建命名元组：
+ 名称
+ 由多个域名组成的字符串，各个域名之间由空格隔开

使用命名元组之前需要加载相关模块，即from collections import nametuple。

from collections import nametuple
# 命名元组名称：DuckT
# 命名元组域名1：bill
# 命名元组域名2：tail
DuckT = namedtuple('DuckT', 'bill tail')
duckt = DuckT('wide orange', 'long')
print duckt       # DuckT(bill='wide orange', tail='long')
print duckt.bill  # wide orange
print duckt.tail  # long

# 使用字典构建命名元组
parts = {'bill': 'wide orange', 'tail': 'long'}
# 关键词变量：**parts
duck2 = DuckT(**parts)
print duck2 # DuckT(bill='wide orange', tail='long')

# 命名元组是不可变的，但是可以替换其中某些域名的值并返回一个新的命名元组
duck3 = duck2._replace(tail='magnificent', bill='crushing')
print duck3 # DuckT(bill='crushing', tail='magnificent')

小结命名元组的优点：

1. 它无论看起来还是用起来都和不可变对象非常相似；
2. 与使用对象相比，使用命名元组在时间和空间上效率更高；
3. 可以使用点好(.)对特性进行访问，而不需要使用字典风格的方括号；
4. 可以把它作为字典的键。

11 实例

11.1 源码

# coding=utf-8
from collections import namedtuple


class Person(object):
    def __init__(self, name):
        self.name = name


class EmailPerson(Person):
    def __init__(self, name, email):
        super(EmailPerson, self).__init__(name)
        # self.name = name
        self.email = email


class MDPerson(Person):
    def __init__(self, name):
        self.name = "Doctor " + name


class JDPerson(Person):
    def __init__(self, name):
        self.name = name + ", Esquire"


class Car():
    def exclaim(self):
        print("I'm a car!")


class Yugo(Car):
    def exclaim(self):
        print "I'm a Yugo! Much like a Car, but more Yugo-ish."

    def need_a_fish(self):
        print "A little help here?"


class Bwm(Car):
    def exclaim(self):
        print("I'm a bwm car!")


class Duck(object):
    """docstring for Duck"""
    def __init__(self, input_name):
        super(Duck, self).__init__()
        self.__name = input_name

    @property
    def name(self):
        print 'inside the getter'
        return self.__name

    @name.setter
    def name(self, input_name):
        print 'inside the setter'
        self.__name = input_name

    # def get_name(self):
    #     print 'inside the getter'
    #     return self.__name

    # def set_name(self, input_name):
    #     print 'inside the setter'
    #     self.__name = input_name

    # name = property(get_name, set_name)


class A(object):
    """docstring for A"""
    count = 0

    def __init__(self):
        super(A, self).__init__()
        A.count += 1

    def exclaim(self):
        print "I'm an A!"

    @classmethod
    def kids(cls):
        print "A has", cls.count, "little objects."


class CoyoteWeapon():
    @staticmethod
    def commercial():
        print "This CoyoteWeapon has been brought to you by Acme."


class Quote():
    def __init__(self, person, words):
        self.person = person
        self.words = words

    def who(self):
        return self.person

    def says(self):
        return self.words + '.'


class QuestionQuote(Quote):
    def says(self):
        return self.words + '?'


class ExclamationQuote(Quote):
    def says(self):
        return self.words + '!'


class BabblingBrook():
    def who(self):
        return 'Brook'

    def says(self):
        return 'Babble'


def who_says(obj):
    print obj.who(), 'says', obj.says()


class Word():
    def __init__(self, text):
        self.text = text

    def __eq__(self, word2):
        return self.text.lower() == word2.text.lower()

    def __str__(self):
        return self.text

    def __repr__(self):
        return 'Word("' + self.text + '")'


class Bill():
    def __init__(self, description):
        self.description = description


class Tail():
    def __init__(self, length):
        self.length = length


class DuckA():
    def __init__(self, bill, tail):
        self.bill = bill
        self.tail = tail

    def about(self):
        print 'This ducka has a ' + self.bill.description + ' bill and a ' + \
            self.tail.length + ' tail.'


if __name__ == '__main__':
    # 类定义
    print '*' * 30, '类定义 ', '*' * 30
    hunter = Person('JohnTian')
    print 'The name of hunter:%s' % hunter.name

    # 继承
    print '*' * 30, ' 继承 ', '*' * 30
    baseCar = Car()
    yugoCar = Yugo()
    baseCar.exclaim()
    yugoCar.exclaim()

    # 覆盖方法
    print '*' * 30, '覆盖方法', '*' * 30
    bwmCar = Bwm()
    baseCar.exclaim()
    bwmCar.exclaim()
    person = Person('jt')
    doctor = MDPerson('jt')
    lawyer = JDPerson('jt')
    print person.name
    print doctor.name
    print lawyer.name

    # 添加新方法
    print '*' * 30, '添加新方法', '*' * 30
    yugoCar.need_a_fish()

    # super
    print '*' * 30, 'super父类方法', '*' * 30
    bob = EmailPerson('bob', 'bob@gmail.com')
    print bob.name
    print bob.email

    print '*' * 30, '类属性的访问和设置', '*' * 30
    fowl = Duck('Howard')
    print fowl.name
    # print fowl.get_name()
    fowl.name = 'johntian'
    print fowl.name
    # fowl.set_name('jt')
    print fowl.name
    # print fowl.__name  # 无法在外部访问__name特性
    print fowl._Duck__name  # 可以在外部访问_Duck__name特性

    print '*' * 30, '方法的类型', '*' * 30
    easy_a = A()
    breezy_a = A()
    wheezy_a = A()
    A.kids()

    print '*' * 30, '鸭子类型', '*' * 30
    hunter = Quote("John tian", "I'm hunting wabbits")
    print hunter.who(), 'says:', hunter.says()

    hunter1 = QuestionQuote("Bugs Bunny", "What's up, doc")
    print hunter1.who(), 'says:', hunter1.says()

    hunter2 = ExclamationQuote("Daffy Duck", "It's rabbit season")
    print hunter2.who(), 'says:', hunter2.says()

    who_says(hunter)
    who_says(hunter1)
    who_says(hunter2)
    brook = BabblingBrook()
    who_says(brook)

    print '*' * 30, '魔术方法', '*' * 30
    first = Word('ha')
    second = Word('HA')
    third = Word('eh')
    print first == second
    print first == third
    # first
    print first

    print '*' * 30, '组合(聚合)', '*' * 30
    tail = Tail('long')
    bill = Bill('wide orange')
    ducka = DuckA(bill, tail)
    ducka.about()

    print '*' * 30, '命名元组', '*' * 30
    # 命名元组名称：DuckT
    # 命名元组域名1：bill
    # 命名元组域名2：tail
    DuckT = namedtuple('DuckT', 'bill tail')
    duckt = DuckT('wide orange', 'long')
    print duckt
    print duckt.bill
    print duckt.tail

    # 使用字典构建命名元组
    parts = {'bill': 'wide orange', 'tail': 'long'}
    # 关键词变量：**parts
    duck2 = DuckT(**parts)
    print duck2

    # 命名元组是不可变的，但是可以替换其中某些域名的值并返回一个新的命名元组
    duck3 = duck2._replace(tail='magnificent', bill='crushing')
    print duck3

11.2 输出

****************************** 类定义  ******************************
The name of hunter:JohnTian
******************************  继承  ******************************
I'm a car!
I'm a Yugo! Much like a Car, but more Yugo-ish.
****************************** 覆盖方法 ******************************
I'm a car!
I'm a bwm car!
jt
Doctor jt
jt, Esquire
****************************** 添加新方法 ******************************
A little help here?
****************************** super父类方法 ******************************
bob
bob@gmail.com
****************************** 类属性的访问和设置 ******************************
inside the getter
Howard
inside the setter
inside the getter
johntian
inside the getter
johntian
johntian
****************************** 方法的类型 ******************************
A has 3 little objects.
****************************** 鸭子类型 ******************************
John tian says: I'm hunting wabbits.
Bugs Bunny says: What's up, doc?
Daffy Duck says: It's rabbit season!
John tian says I'm hunting wabbits.
Bugs Bunny says What's up, doc?
Daffy Duck says It's rabbit season!
Brook says Babble
****************************** 魔术方法 ******************************
True
False
ha
****************************** 组合(聚合) ******************************
This ducka has a wide orange bill and a long tail.
****************************** 命名元组 ******************************
DuckT(bill='wide orange', tail='long')
wide orange
long
DuckT(bill='wide orange', tail='long')
DuckT(bill='crushing', tail='magnificent')
[Finished in 0.1s]

参考

Python语言及其应用 第六章