Python魔术方法专题

class Bar(object):
  def __del__(self):
    print("被回收了！ ～")


a = Bar()

a.__del__() # 主动调用是没用的，因为引用计数不为零，并不会回收资源 gc
print("已经删除a了")
print(a)

del a
# print(a)

class Bar(object):
  __slots__ = ('name', 'gender')

  def __init__(self, name='monkey'):
    self.name = name
    self.gender = 'male'


a = Bar()
a.age = 18  # 动态添加属性是会报错的。
print(a.name)

class Bar(object):

  def __str__(self):
    return "Bar"


a = Bar()
print(a) # Bar

class Bar(object):
  name = 'monkey'


a = Bar()
print(a.__class__.name)  # 允许通过实例化对象访问类

class Bar(object):
  """
  A simple show class!
  """
  name = 'monkey'

  def get_name(self):
    """
    get class argument name
    """
    return self.__class__.name


a = Bar()
print(a.__class__.__doc__)
print(a.__class__.get_name.__doc__)

#  A simple show class!
#  
#
#    get class argument name

class Lady(object):
  """ """

class Small(object):
  """ """

class SmallLady(Small, Lady):
  """"""


print(Lady.__base__)  # <class 'object'>
print(SmallLady.__bases__)  # (<class '__main__.Small'>, <class '__main__.Lady'>)

class ListMeta(type):
  def __call__(self, data, *args, **kwargs):  # 使得self 也就是实例化出的类 是可调用的 List() 这里的self指的是 将要 实例化出来的类 本身
    self.__init__(self,data)
    return self

  def __str__(self):
    result = self.clean_data(self) # 是 List 可以返回期望的列表格式 将对象转化为对人友好的字符串
    result = '[{}]'.format(result[:-1])
    return result

  def __repr__(self):
    return 'List({})'.format(self.__str__())  # 转化为对解释器友好的字符串

  def __iter__(self):		# 返回实现了迭代器协议的对象
    return self # 它本身实现了 __next__

  def __next__(self):		# 实现迭代器协议，每次返回下一个值 或 一个迭代异常终止迭代
    if self.index >= len(self.data):  
      raise StopIteration
    else:
      value = self.data[self.index]
      self.index += 1
      return value

  def __len__(self):  # 返回对象的长度，len()函数会执行对象的 __len__方法
    return self.len


class List(metaclass=ListMeta):

  def __init__(self, data):
    self.data = data
    self.index = 0
    self.len = len(self.data)
    

l = List([1,2,3,4,5,6,7])

print(l)
print(len(l))

for i in l:
  print(i)

class Storage(object):

  def __init__(self, name):
    self.name = name  # 调用__setattr__方法

  def __getattribute__(self, item):  # 每个属性访问前都先调用该方法
    print('getattribute: %s' % item)
    ret = True
    if item == 'error':
      raise AttributeError(r'Error ~ "error"')  # 报错了依然执行～ 
    else:
      ret = object.__getattribute__(self, item)
    return ret

  def __getattr__(self, item):
    print('getattr: %s' % item)
    try:
      return self.__dict__[item]
    except (IndexError, KeyError)as e:
      print('No attribute %s ' % e)
    return '%s is error' % item

  def __setattr__(self, key, value):
    print('setattr: %s ' % key)
    self.__dict__.update({key:value})


file = Storage('file')
name = file.error  # 调用 __getattr__ 方法
# setattr: name 
# getattribute: __dict__
# getattribute: error
# getattr: error
# getattribute: __dict__
# No attribute 'error'