python学习-面向对象3

class Foo(object):
    pass

obj = Foo()

if isinstance(obj,Foo):
    print(‘Yes‘)
else:
    print(‘No‘)

class B(object):
    pass

class C(B):
    pass

print(issubclass(C, B))

class MyDict(dict):

    def __init__(self):
        self.__li = []
        super(MyDict,self).__init__()


    def __setitem__(self, key, value):
        self.__li.append(key)
        super(MyDict,self).__setitem__(key, value)

    def __str__(self):
        temp_list = []
        for key in self.__li:
            temp_list.append("\‘%s\‘: %s" % (key,self.__getitem__(key)))
        temp_str ="{" + ",".join(temp_list) + "}"
        return temp_str


obj = MyDict()
obj[‘k1‘] = ‘v1‘
obj[‘k2‘] = ‘v2‘

print(obj)

try:
    # 逐行执行主代码段
    print(123)
except ValueError as ex:
    # 当检测到 ValueError 时执行
    print(ex)
except Exception as ex:
    # Exception 匹配所有一样
    # 当检测到除 ValueError 之外的错误时执行
    print(ex)
else:
    # 当主代码块执行完成后执行
    pass
finally:
    # 无论主代码块是否有报错，都执行
    pass

try:
    raise Exception(‘主动错误一下‘)
except Exception as e:
    print(e)

class MyException(Exception):

    def __init__(self, msg):
        self.message = msg

    def __str__(self):
        return self.message


try:
    raise MyException("主动错一下自定义的错误")
except MyException as e:
    print(e)

# 当 assert 后面的表达式为 True 时不报错，否则报 AssertionError 错误
assert 1 == 1
assert 1 == 2

class ConnectPool(object):

    __pool = None

    def __init__(self):
        pass

    @staticmethod
    def get_pool():
        if not ConnectPool.__pool:
            ConnectPool.__pool = ConnectPool()
        return ConnectPool.__pool



obj1 = ConnectPool.get_pool()
obj2 = ConnectPool.get_pool()

print(obj1,obj2)