[Antoine]
> I agree with David that copy(os.environ) is rather ambiguous.
> I think the preferred idiom should be to call dict(os.environ).
> As for __copy__, I don't know what it should do: perhaps
> simply raise an error when copying is attempted?

FWIW, I concur with Antoine on every point.  Also, raising an error when copying seems reasonable ("refuse the temptation to guess" at what the user intended).