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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
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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")
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