I think returning sys.{maxint,maxsize} in this case is a plain lie.
That's not practicality, that's giving back false information.

Barring drastic language changes (such as having objects representing
"infinity" or "greater than" - which, of course, won't happen), I think
the current behaviour of raising an exception is the correct one. But,
although I think OverflowError is good enough, the current exception
message is a bit cryptic, especially for anyone who doesn't know C:

"""OverflowError: Python int too large to convert to C ssize_t"""

I've attached a simple patch (modified from Alexander's) to raise:

"""OverflowError: Length too large"""

(I thought about "Object too large", but our problem is actually that
the *length* itself is too large)