Paul Ganssle: Even if Andrew were not suggesting adding copy to the C implementation (I have no opinion on that currently), it would still be correct to maintain backward compatibility in the python version in the standard library.  We do not consider the standard library to be CPython specific, even though parts of it are.  There is no "fork" involved in other projects using it, from our point of view.  Quite the opposite, where possible.  We have given commit rights to developers from other python implementations specifically so they can contribute things that improve compatibility in the standard library and standard library test suite for those other python implementations.