Unfortunately, long/float comparison doesn't work quite correctly right now:
n = 1 for i in range(2000): n += n n == 0.0 OverflowError: long int too large to convert to float
One strategy for solving the problem is to observe that for every floating-point implementation, there is a number N with the property that if x >= N, converting x from float to long preserves information, and if x <= N, converting x from long to float preserves information. Therefore, instead of unconditionally converting to float, the conversion's direction should be based on the value of one of the comparands.
Of course, such comparisons can be made faster by doing a rough range check first, and doing the actual conversion only if the number of bits in the long is commensurate with the exponent of the float.
Do you think you can come up with a patch, or at least a description of an algorithm that someone without a wizard level understanding of the issues could implement? --Guido van Rossum (home page: http://www.python.org/~guido/)