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Fair enough - it sounds like the additional methods, if
any, should be kept to a minimum, and some of the other
stuff that I want to do should maybe be in an add-on module
rather than an addition to the core language. if/When I have
some
time I'll write a PEP for the methods and maybe another one
for the array-of-bit support , or bitstream, or whatever it
winds up being. A goal here is to be able to do
variable-length coding/decoding in Python without
being too slow; if I can think up a more general-purpose
thing that  can do that, so much the better.

popcount I hadn't heard of, but Google just found it
for me in a Java lib. Definitely fits into the class of
things-which-go-much-faster-in-C. And yes, it makes a 
lot of sense to do this to ints and longs uniformly.