Python内置函数(65)——type

英文文档:

class type(object)

class type(name, bases, dict)

With one argument, return the type of an object. The return value is a type object and generally the same object as returned by object.__class__.

The isinstance() built-in function is recommended for testing the type of an object, because it takes subclasses into account.

With three arguments, return a new type object. This is essentially a dynamic form of the class statement. The name string is the class name and becomes the __name__ attribute; the bases tuple itemizes the base classes and becomes the __bases__ attribute; and the dict dictionary is the namespace containing definitions for class body and is copied to a standard dictionary to become the __dict__ attribute.

说明:

  1. 函数只传入一个参数时,返回参数对象的类型。 返回值是一个类型对象,通常与对象.__ class__返回的对象相同。

#定义类型A
>>> class A:
name = 'defined in A' #创建类型A实例a
>>> a = A() #a.__class__属性
>>> a.__class__
<class '__main__.A'> #type(a)返回a的类型
>>> type(a)
<class '__main__.A'> #测试类型
>>> type(a) == A
True

  2. 虽然可以通过type函数来检测一个对象是否是某个类型的实例,但是更推荐使用isinstance函数,因为isinstance函数考虑了父类子类间继承关系。

#定义类型B,继承A
>>> class B(A):
age = 2 #创建类型B的实例b
>>> b = B() #使用type函数测试b是否是类型A,返回False
>>> type(b) == A
False #使用isinstance函数测试b是否类型A,返回True
>>> isinstance(b,A)
True

  3. 函数另一种使用方式是传入3个参数,函数将使用3个参数来创建一个新的类型。其中第一个参数name将用作新的类型的类名称,即类型的__name__属性;第二个参数是一个元组类型,其元素的类型均为类类型,将用作新创建类型的基类,即类型的__bases__属性;第三个参数dict是一个字典,包含了新创建类的主体定义,即其值将复制到类型的__dict__属性中。

#定义类型A,含有属性InfoA
>>> class A(object):
InfoA = 'some thing defined in A' #定义类型B,含有属性InfoB
>>> class B(object):
InfoB = 'some thing defined in B' #定义类型C,含有属性InfoC
>>> class C(A,B):
InfoC = 'some thing defined in C' #使用type函数创建类型D,含有属性InfoD
>>> D = type('D',(A,B),dict(InfoD='some thing defined in D')) #C、D的类型
>>> C
<class '__main__.C'>
>>> D
<class '__main__.D'> #分别创建类型C、类型D的实例
>>> c = C()
>>> d = D() #分别输出实例c、实例b的属性
>>> (c.InfoA,c.InfoB,c.InfoC)
('some thing defined in A', 'some thing defined in B', 'some thing defined in C')
>>> (d.InfoA,d.InfoB,d.InfoD)
('some thing defined in A', 'some thing defined in B', 'some thing defined in D')
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