[Python-Dev] PyObject_IsInstance is dangerous

[Greg Ewing]

Serhiy Storchaka wrote:
> PyObject_IsInstance is not safe when used to check if the object is an 
> instance of specified builtin type.
> 
> The __class__ attribute can be modified and PyObject_IsInstance() can 
> return true if the object has not layout compatible with specified 
> structure.

Code that requires a particular C layout should be using
PyObject_TypeCheck, not PyObject_IsInstance.

-- 
Greg