Question

有没有办法根据传递的变量动态更改对象类？例如：

class Parent:
    def __init__(self, variable):
        ...
        some magic
        ...

class ChildA:
    pass

class ChildB:
    pass


cls=Parent('a')
cls.__class__
<class '__main__.ChildA'>

cls=Parent('b')
cls.__class__
<class '__main__.ChildB'>

Answer 1

这可以在Parent类的__new__方法中完成。它可以决定实际创建的对象：

class Parent(object):
    def __new__(cls, selector):
        if selector == 'a':
            return object.__new__(A)
        else:
            return object.__new__(B)

class A(Parent):
    letters = 'aaaaa'

class B(Parent):
    letters = 'bbbbb'

a = Parent('a')
print(a.letters)
b = Parent('b')
print(b.letters)

输出证明它有效：

aaaaa
bbbbb

Answer 2

在__new__之前的父级的__init__函数中定义条件检查if。

class Parent(Object):
   def __new__(self,s):
       if s=='a':
         return object.__new__(childA)
       else:
         return object.__new__(childB)
class childA(Parent):
   pass
class childB(Parent):
   pass

Python类取决于变量

2 个答案: