set intersection_update, difference_update, symmetric_difference_update should check self is equal to given arg #3881

Feature

They are also relevant to inplace operations( iand, isub, ixor ).
CPython checks whether given argument and selfobject are equal and then returns.

• intersection_update : If self == arg, returns self.copy()
• difference_update : If self == arg, returns self.clear(); Ok(())
• symmetric_difference_update : If self == arg, returns self.clear(); Ok(())

At the current implementation, they get a parameter as SetIterable which is converted from PyObjectRef before entering each method.
For checking self == arg, we should convert it after checking.

Python Documentation

• https://github.com/python/cpython/blob/3.10/Objects/setobject.c#L1627-L1630
• https://github.com/python/cpython/blob/3.10/Objects/setobject.c#L1410-L1412
• https://github.com/python/cpython/blob/3.10/Objects/setobject.c#L1186-L1189

Relevant Test Case

• test_set.py test_inplace_on_self