python - 更改 python 对象的类(强制转换)

Question

关于这个python doc page它说:

Like its identity, an object’s type is also unchangeable.

我试试这个脚本，

#!python3  

class Foo:
  num = 1
  pass

class Bar:
  num = 2
  pass

f1,f2= Foo(), Foo()

f2.__class__ = Bar
print( type(f1), type(f2), f1.num, f2.num )

结果显示:

<class '__main__.Foo'> <class '__main__.Bar'> 1 2

我想我改变了type的 f2 .
怎么了，我错过了什么？

Answer 1

该页的脚注:

[1] It is possible in some cases to change an object’s type, under certain controlled conditions. It generally isn’t a good idea though, since it can lead to some very strange behaviour if it is handled incorrectly.

如果你尝试将f2的__class__改为list:

f2.__class__ = list

引发类型错误:

TypeError: __class__ assignment: only for heap types