More pythonic circle?

[John Machin]

OTTOMH, in a rush to go out: never mind Pythonic, following apply to
any language:
(1) accuracy: (a) sue me if I'm wrong, but I think you need range(dx+1)
so that the dx pixel is filled in (b) a few more digits after 0.71
might be useful
(2) efficiency: seems that range(dy, dx+1) would save some wear & tear
on the circuitry :-)
(3) legibility: there's no prize for the script with the absolutely
minimum number of space characters :-)
I think I've got an article on better Bresenham somewhere in the
archives; will dig it out later.
Cheers,
John