In following teststr.py, class MyString is nestedly instanced in method __getattr__(). This script will lead to a  "core dump" in Python interpreter.  My Python version is  3.9.1 and my operating system is Ubuntu 16.04. 

teststr.py
+++++++++++++++++++++++++++++++++++++++++++
class StrError(str):
    pass

class MyString:

    def __init__(self, istr):
        self.__mystr__ = istr

    def __getattr__(self, content):
        with self:
            return MyString(getattr(self.__mystr__, content))

    def __setattr__(self, content, sstr):
        setattr(self.__mystr__, content)

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
         raise StrError(self.__mystr__) 
         return True

MyString("hello")
+++++++++++++++++++++++++++++++++++++++++