Python面向对象魔法方法和单例模块代码实例

class Uderline_func:

  x = 100
  
  def __init__(self, y):
    print('类加括号调用的时候触发我！')
    self.y = y # 当与__setattr__方法同时存在时，self.y = y并不会被加载到对象的名称空间
    # self['y'] = y # TypeError: 'Uderline_func' object does not support item assignment
  def general_func(self):
  
    print('随便定义的一个函数！')


  # def __getattr__(self, item):
  #   print('只有对象获取一个没有的属性值得时候触发我！')
  
  def __getattribute__(self, item):
  
    print('类或对象无论获取的属性有没有都会触发我！且出现我，对象点一个没有的属性会覆盖掉__getattr__，还会导致__setattr__函数报错')
  
  def __setattr__(self, key, value):
  
    print('设置属性的时候触发我！')
    # self.a = '在对象名称空间增加一个值！' # 会一直触发__setattr__,出现递归调用
    self.__dict__['a'] = '在对象名称空间增加一个值！'
  def __delattr__(self, item):
  
    print('删除值得时候触发我！')
  
  def __del__(self):
  
    print('程序运行完，被Python解释器回收时，触发我！')
# print(Uderline_func.__dict__) # 类在定义阶段就已经创建好了类名称空间，将其内部变量名和函数名塞进去
u = Uderline_func(100) # 触发__init__
# print(u.__dict__) # {'y': 100}
# Uderline_func.z # 只会触发__getattribute__
u.z # 获取没有的属性触发__getattr__
# u.name = 'zhang' # 触发__setattr__
# del u.x # 对象不能删除掉类中的属性，但只要执行删除操作，都会触发__delattr__的执行

class Uderline_func():
  x = 100
  # def __new__(cls, *args, **kwargs):
  #
  #   print('在__init__执行之前触发我，造一个空对象！')
  def __init__(self):
    print('类加括号调用的时候触发我！')
  def __call__(self, *args, **kwargs):
    print('对象加括号调用的时候触发我！')
  def __str__(self):
    print('对象被打印的时候触发我！')
    return '必须要写return返回一个字符串！不然报错"TypeError: __str__ returned non-string (type NoneType)"'
u = Uderline_func()
u()
print(u)

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

  def __getitem__(self, item):
    print(self.__dict__[item])

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

    # self.age = value # 也可以给对象添加属性


  def __delitem__(self, key):
    print('del obj[key]时,我执行')
    self.__dict__.pop(key)
  def __delattr__(self, item):
    print('del obj.key时,我执行')
    self.__dict__.pop(item)
f1=Foo('sb')
f1['age']=18
# print(f1.__dict__)
f1['age1']=19
# del f1.age1
# del f1['age']
f1['name']='alex'
f1.xxx = 111
print(f1.__dict__) # {'name': 'alex', 'age': 18, 'age1': 19, 'xxx': 111}

class Foo:
  __slots__ = 'x'
f1 = Foo()
f1.x = 1
f1.y = 2 # 报错
print(f1.__slots__) # f1不再有__dict__属性
print(f1.x) #依然能访问
class Bar:
  __slots__ = ['x', 'y']
n = Bar()
n.x, n.y = 1, 2
n.z = 3 # 报错

class Foo:
  '我是描述信息'
  pass
print(Foo.__doc__)
class Foo:
  '我是描述信息'
  pass

class Bar(Foo):
  pass
print(Bar.__doc__) #该属性无法继承给子类

class C:
  def __init__(self):
    self.name = ‘SB'
from lib.aa import C
obj = C()
print obj.__module__ # 输出 lib.aa，即：输出模块
print obj.__class__   # 输出 lib.aa.C，即：输出类

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

  def __enter__(self):
    print('出现with语句,对象的__enter__被触发,有返回值则赋值给as声明的变量')
    # return self
  def __exit__(self, exc_type, exc_val, exc_tb):
    print('with中代码块执行完毕时执行我啊')

with Open('a.txt') as f:
  print('=====>执行代码块')
  # print(f,f.name)
  
'''
出现with语句,对象的__enter__被触发,有返回值则赋值给as声明的变量
=====>执行代码块
with中代码块执行完毕时执行我啊
'''

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

  def __enter__(self):
    print('出现with语句,对象的__enter__被触发,有返回值则赋值给as声明的变量')

  def __exit__(self, exc_type, exc_val, exc_tb):
    print('with中代码块执行完毕时执行我啊')
    print(exc_type)
    print(exc_val)
    print(exc_tb)


with Open('a.txt') as f:
  print('=====>执行代码块')
  raise AttributeError('***着火啦,救火啊***')
print('0'*100) #------------------------------->不会执行


'''
出现with语句,对象的__enter__被触发,有返回值则赋值给as声明的变量
=====>执行代码块
with中代码块执行完毕时执行我啊
<class 'AttributeError'>
***着火啦,救火啊***
<traceback object at 0x000000000A001E88>
Traceback (most recent call last):
 File "G:/Python代码日常/第一阶段/1阶段/面向对象/test.py", line 52, in <module>
  raise AttributeError('***着火啦,救火啊***')
AttributeError: ***着火啦,救火啊***

'''

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

  def __enter__(self):
    print('出现with语句,对象的__enter__被触发,有返回值则赋值给as声明的变量')

  def __exit__(self, exc_type, exc_val, exc_tb):
    print('with中代码块执行完毕时执行我啊')
    print(exc_type)
    print(exc_val)
    print(exc_tb)
    return True
  with Open('a.txt') as f:
  print('=====>执行代码块')
  raise AttributeError('***着火啦,救火啊***')
print('0'*100) #------------------------------->会执行

class Open:
  def __init__(self,filepath,mode='r',encoding='utf-8'):
    self.filepath=filepath
    self.mode=mode
    self.encoding=encoding

  def __enter__(self):
    # print('enter')
    self.f=open(self.filepath,mode=self.mode,encoding=self.encoding)
    return self.f

  def __exit__(self, exc_type, exc_val, exc_tb):
    # print('exit')
    self.f.close()
    return True 
  def __getattr__(self, item):
    return getattr(self.f,item)

with Open('a.txt','w') as f:
  print(f)
  f.write('aaaaaa')
  f.wasdf #抛出异常，交给__exit__处理

# @classmethod(用类绑定方法)

import settings

class MySQL:
  __instance=None
  def __init__(self, ip, port):
    self.ip = ip
    self.port = port
  @classmethod
  def from_conf(cls):
    if cls.__instance is None:
      cls.__instance=cls(settings.IP, settings.PORT)
    return cls.__instance
obj1=MySQL.from_conf()
obj2=MySQL.from_conf()
obj3=MySQL.from_conf()
# obj4=MySQL('1.1.1.3',3302)
print(obj1)
print(obj2)
print(obj3)
# print(obj4)

# 用类装饰器
import settings

def singleton(cls):
 _instance=cls(settings.IP,settings.PORT)
 def wrapper(*args,**kwargs):
   if len(args) !=0 or len(kwargs) !=0:
     obj=cls(*args,**kwargs)
     return obj
   return _instance
 return wrapper

@singleton #MySQL=singleton(MySQL) #MySQL=wrapper
class MySQL:
 def __init__(self, ip, port):
   self.ip = ip
   self.port = port

# obj=MySQL('1.1.1.1',3306) #obj=wrapper('1.1.1.1',3306)
# print(obj.__dict__)

obj1=MySQL() #wrapper()
obj2=MySQL() #wrapper()
obj3=MySQL() #wrapper()
obj4=MySQL('1.1.1.3',3302) #wrapper('1.1.1.3',3302)
print(obj1)
print(obj2)
print(obj3)
print(obj4)

# 调用元类
import settings

class Mymeta(type):
  def __init__(self,class_name,class_bases,class_dic):
    #self=MySQL这个类
    self.__instance=self(settings.IP,settings.PORT)

  def __call__(self, *args, **kwargs):
    # self=MySQL这个类
    if len(args) != 0 or len(kwargs) != 0:
      obj=self.__new__(self)
      self.__init__(obj,*args, **kwargs)
      return obj
    else:
      return self.__instance

class MySQL(metaclass=Mymeta): #MySQL=Mymeta(...)
  def __init__(self, ip, port):
    self.ip = ip
    self.port = port
obj1=MySQL()
obj2=MySQL()
obj3=MySQL()
obj4=MySQL('1.1.1.3',3302)
print(obj1)
print(obj2)
print(obj3)
print(obj4)

# 利用模块多次导入只产生一次名称空间，多次导入只沿用第一次导入成果。
def f1():
  from singleton import instance
  print(instance)

def f2():
  from singleton import instance,My
  SQL
  print(instance)
  obj=MySQL('1.1.1.3',3302)
  print(obj)

f1()
f2()