Python面向对象-魔术方法

class Programer():
    def __new__(cls,*args,**kwargs):
        print('call __new__ method')
        print(args)
        return super(Programer,cls).__new__(cls)

    def __init__(self,name,age):
        print('call __init__ method')
        self.name = name
        self.age = age

if __name__ == '__main__':
    programer = Programer('Albert',25)
    print(programer.__dict__)

call __new__ method
('Albert', 25)
call __init__ method
{'name': 'Albert', 'age': 25}

class Programer(object):
    def __init__(self,name,age):
        self.name = name
        if isinstance(age,int):
            self.age = age
        else:
            raise Exception('age must be int')

    def __eq__(self,other):
        if isinstance(other,Programer):        # 首先判断是否Programer对象
            if self.age == other.age:
                return True
            else:
                return False
        else:
            raise Exception('The type of object must be Programer')

    def __add__(self,other):
        if isinstance(other,Programer):
            return self.age + other.age
        else:
            raise Exception('The type of object must be Programer')

if __name__ == '__main__':
    p1 = Programer('Albert',25)
    p2 = Programer('Bill',30)
    print(p1==p2)
    print(p1+p2)

False
55

class Programer(object):
    def __init__(self,name,age):
        self.name = name
        if isinstance(age,int):
            self.age = age
        else:
            raise Exception('age must be int')

    def __str__(self):
        return '%s is %s years old'%(self.name,self.age)

    def __dir__(self):
        return self.__dict__.keys()

if __name__ == '__main__':
    p = Programer('Albert',25)
    print(p)
    print(dir(p))

Albert is 25 years old
['age', 'name']

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

    def __getattribute__(self,name):
        # return getattr(self,name) # 会产生无限递归
        # 调用父类的getattribute方法，不会产生无限递归
        return super(Programer,self).__getattribute__(name) 

    def __setattr__(self,name,value):
        # setattr(self,name,value) # 会产生无限递归
        self.__dict__[name] = value

if __name__ == '__main__':
    p = Programer('Albert',25)
    print(p.name)

Albert

class Student(object):
    __slots__ = ('name', 'gender', 'score')
    def __init__(self, name, gender, score):
        self.name = name
        self.gender = gender
        self.score = score

>>> s = Student('Bob', 'male', 59)
>>> s.name = 'Tim' # OK
>>> s.score = 99 # OK
>>> s.grade = 'A'
Traceback (most recent call last):
  ...
AttributeError: 'Student' object has no attribute 'grade'

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

class Student(Person):
    __slots__ = ('score',)
    def __init__(self, name, gender, score):
        super(Student, self).__init__(name, gender)
        self.score = score

s = Student('Bob', 'male', 59)
s.name = 'Tim'
s.score = 99
print s.score

class FunctionalList:
    '''一个列表的封装类，实现了一些额外的函数式
    方法，例如head, tail, init, last, drop和take。'''

    def __init__(self, values=None):
        if values is None:
            self.values = []
        else:
            self.values = values

    def __len__(self):
        return len(self.values)

    def __getitem__(self, key):
        # 如果键的类型或值不合法，列表会返回异常
        return self.values[key]

    def __setitem__(self, key, value):
        self.values[key] = value

    def __delitem__(self, key):
        del self.values[key]

    def __iter__(self):
        return iter(self.values)

    def __reversed__(self):
        return reversed(self.values)

    def append(self, value):
        self.values.append(value)

    def head(self):
        # 取得第一个元素
        return self.values[0]

    def tail(self):
        # 取得除第一个元素外的所有元素
        return self.valuse[1:]

    def init(self):
        # 取得除最后一个元素外的所有元素
        return self.values[:-1]

    def last(self):
        # 取得最后一个元素
        return self.values[-1]

    def drop(self, n):
        # 取得除前n个元素外的所有元素
        return self.values[n:]

    def take(self, n):
        # 取得前n个元素
        return self.values[:n]

with open('foo.txt') as bar:
    # 使用bar进行某些操作

class Closer:
    '''一个上下文管理器，可以在with语句中
    使用close()自动关闭对象'''

    def __init__(self, obj):
        self.obj = obj

    def __enter__(self, obj):
        return self.obj # 绑定到目标

    def __exit__(self, exception_type, exception_value, traceback):
        try:
                self.obj.close()
        except AttributeError: # obj不是可关闭的
                print 'Not closable.'
                return True # 成功地处理了异常

>>> from magicmethods import Closer
>>> from ftplib import FTP
>>> with Closer(FTP('ftp.somesite.com')) as conn:
...         conn.dir()
...
# 为了简单，省略了某些输出
>>> conn.dir()
# 很长的 AttributeError 信息，不能使用一个已关闭的连接
>>> with Closer(int(5)) as i:
...         i += 1
...
Not closable.
>>> i
6

import time

class Slate:
        '''存储一个字符串和一个变更日志的类
        每次被pickle都会忘记它当前的值'''

        def __init__(self, value):
                self.value = value
                self.last_change = time.asctime()
                self.history = {}

        def change(self, new_value):
                # 改变当前值，将上一个值记录到历史
                self.history[self.last_change] = self.value
                self.value = new_value)
                self.last_change = time.asctime()

        def print_change(self):
                print 'Changelog for Slate object:'
                for k,v in self.history.items():
                        print '%s\t %s' % (k,v)

        def __getstate__(self):
                # 故意不返回self.value或self.last_change
                # 我们想在反pickle时得到一个空白的slate
                return self.history

        def __setstate__(self):
                # 使self.history = slate，last_change
                # 和value为未定义
                self.history = state
                self.value, self.last_change = None, None