It would be nice if all numbers could be used as arrays
of bits as well.

Example:

>>> i = 10
>>> i[0] = 1
>>> print i
11
>>> print list(i)
[1, 1, 0, 1]
>>> "".join(map(lambda b:str(b), l))
'1101'
>>> for bit in i: print bit
1
1
0
1

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Allowing assignments like i[o]=1 can only work for mutable
objects.   Since int is immutable, your idea would need to
be implemented as a separate extension class.

I recommend writing it first in pure python and posting it
as a cookbook recipe.  After it matures (possibly growing
other bit twiddling methods such as countbits) and has a fan
club (with some real world applications), it might warrant
coding in C.

From my experience with the setmodule, I can say that this
is not a trivial understanding, so you really have to be
sure you've worked out the API and that it meets real needs.