[Python-Dev] PyObject_IsInstance is dangerous

Greg Ewing greg.ewing at canterbury.ac.nz
Mon May 18 14:14:24 CEST 2015

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.


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