I didn't know about issues with pickling. As for the performance issue, is date.isocalendar() really performance critical?

I found a precedent for replacing a tuple by a namedtuple: https://hg.python.org/cpython/rev/ef72142eb8a2

I'm trying my hand at writing a patch (I'm a new contributor) but it seems the code is implemented twice: both in Lib/ (python) and in Modules/ (C). I'm having a hard time figuring out how to conjure up a namedutple from the C code. Any hepl is appreciated.

Thanks.