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目录type示例isinstance示例issubclass示例综合示例isinstance针对类issubclass总结type type方法有两种重载形式: type(o: ob
type
方法有两种重载形式:
type(o: object)
;type(name: str, bases:Tuple[type, ...], dict:Mapping[str: Any], **kwds)
使用第一种重载形式的时候,传入一个【object】类型,返回一个【type】对象,通常与object.__class__
方法的返回值相同。
使用第二种重载形式的时候,也会得到一个【type】对象,本质上来说这是一种动态类,参数含义如下:
__name__
属性;__bases__
属性;__dict__
属性;重载形式1
class A(object):
pass
a = A()
print(type(a), a.__class__, type(A))
-----------------------------
<class '__main__.A'> <class '__main__.A'> <class 'type'>
重载形式2
class OldClass(object):
a = 1
def __init__(self) -> None:
self.name = "OldClass"
def get_name(self):
return self.name
my_dynamic_cls = type('DynamicClass', (OldClass,),
dict(name='dynamic', a=2, b=3, c=4))
new_obj = my_dynamic_cls()
print(my_dynamic_cls.__dict__)
print(new_obj.__dict__, type(new_obj))
-----------------------------
{'name': 'dynamic', 'a': 2, 'b': 3, 'c': 4, '__module__': '__main__', '__doc__': None}
{'name': 'OldClass'} <class '__main__.DynamicClass'>
在上面的示例中我们使用type
成功创造了一个动态类并添加了几个类属性,由于指定了【OldClass】作为父类,所以动态生成的类也具有【OldClass】的全部特性。
动态生成一个类的时候不光可以指定类属性,还可以绑定类方法,示例如下:
class OldClass(object):
a = 1
def __init__(self) -> None:
self.name = "OldClass"
def get_name(self):
return self.name
def print_msg(msg: str) -> None:
print(msg)
my_dynamic_cls = type('DynamicClass ', (OldClass,),
dict(name='dynamic', a=2, b=3, c=4, method=print_msg))
new_obj = my_dynamic_cls()
my_dynamic_cls.method("使用动态绑定的方法!!")
print(my_dynamic_cls.__dict__)
-----------------------------
使用动态绑定的方法!!
{'name': 'dynamic', 'a': 2, 'b': 3, 'c': 4, 'method': <function print_msg at 0x00000188189F73A0>, '__module__': '__main__', '__doc__': None}
Return True if the object argument is an instance of the classinfo argument, or of a (direct, indirect, or virtual) subclass thereof. If object is not an object of the given type, the function always returns False. If classinfo is a tuple of type objects (or recursively, other such tuples) or a uNIOn of multiple types, return True if object is an instance of any of the types. If classinfo is not a type or tuple of types and such tuples, a TypeError exception is raised. TypeError may not be raised for an invalid type if an earlier check succeeds.
——pythonDoc
isinstance
方法用来检查给定的对象是否是给定类型的实例或者是给定类型的任意子类的实例,通常使用该方法进行对象类型校验。
class AMetaClass(type):
def __new__(cls, *args, **kwargs):
return type.__new__(cls, *args, **kwargs)
class BMetaClass(AMetaClass):
pass
class AClass(object, metaclass=BMetaClass):
def __init__(self, name: str) -> None:
self.name = name
class BClass(AClass):
def __init__(self, name: str) -> None:
super().__init__(name)
obj_a = AClass('a')
obj_b = BClass('b')
-----------------------------
print(isinstance(obj_b, AClass)) -> True
print(isinstance(obj_b, BClass)) -> True
print(isinstance(obj_b, AMetaClass)) -> False
print(isinstance(obj_b, BMetaClass)) -> False
print(isinstance(obj_b, type)) -> False
print(isinstance(BClass, AMetaClass)) -> True
print(isinstance(BClass, BMetaClass)) -> True
print(isinstance(BClass, type)) -> True
总结一下,isinstance
方法检查的范围就是参数的模板层按照继承关系进行检索。
issubclass(class: type, classinfo: Union[type, ...])
方法用来判断指定的两个类型之间的从属关系,如果【class】是【classinfo】的子类返回真(True),否则返回假(False)。
有几点注意事项这里说一下:
issubclass(cls, cls)
返回是真; class AMetaClass(type):
def __new__(cls, *args, **kwargs):
return type.__new__(cls, *args, **kwargs)
class BMetaClass(AMetaClass):
pass
class AClass(object, metaclass=BMetaClass):
def __init__(self, name: str) -> None:
self.name = name
class BClass(AClass):
def __init__(self, name: str) -> None:
super().__init__(name)
obj_a = AClass('a')
obj_b = BClass('b')
-----------------------------
issubclass(AMetaClass, type) -> True
issubclass(BMetaClass, type) -> True
issubclass(BMetaClass, AMetaClass) -> True
issubclass(AClass, AMetaClass) -> False
issubclass(AClass, BMetaClass) -> False
issubclass(BClass, AClass) -> True
issubclass(AClass, obj_a) -> TypeError: arg 2 must be a class
issubclass(obj_a, AClass) -> TypeError: arg 1 must be a class
从程序结果可以看到传入元类和类返回永远是假,并且不能直接传入对象。
为了更好的让大家明白这三者之间的区别和联系,我画了一张图
这是初始状态,定义了三个对象,三个类和三个元类,它们之间的关系如上图所示;
class M1(type):
def __new__(cls, *args, **kwargs):
return type.__new__(cls, *args, **kwargs)
class M2(M1):
pass
class M3(type):
def __new__(cls, *args, **kwargs):
return type.__new__(cls, *args, **kwargs)
class C1(metaclass=M3):
pass
class C2(C1):
pass
class C3(metaclass=M2):
pass
o1 = C1()
o2 = C2()
o3 = C3()
针对对象
以【O2】为例,它的检索范围如下图红线所示:
以【C3】为例,它的检索范围如下图红线所示:
针对类
以【C2】为例,返回真值的范围如下:
针对元类
以【M2】为例,返回真值的范围如下:
调用type
方法
调用isinstance
方法
调用issubclass
方法
以上就是一文带你了解Python中的type,isinstance和issubclass的详细内容,更多关于Python type isinstance issubclass的资料请关注编程网其它相关文章!
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