I suspect the last big hurdle to making built-in data structures nicely subclassable is the insistence of such types to return new instances as the base class instead of the derived class.
In case that wasn't clear ;) --> class MyInt(int): ... def __repr__(self): ... return 'MyInt(%d)' % self ... --> m = MyInt(42) --> m MyInt(42) --> m + 1 43 --> type(m+1) <class 'int'> Besides the work it would take to rectify this, I imagine the biggest hurdle would be the performance hit in always looking up the type of self. Has anyone done any preliminary benchmarking? Are there other concerns? -- ~Ethan~
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