I was noticing that in some situations floor division (the // operator) seems to behave incorrectly. Here is one example:
>>> 59 // 0.2
294.0
Two things - one, the answer is just wrong. The correct answer is 295 (note that 59 / 0.2 gives the correct result of 295.0). The second issue is that this result is a float, not an integer.
I cannot for the life of me figure out how this is happening. Is it a bug? Some weird behavior when a float is in the divisor? I am using 3.12.
When you use 0.2 in source code, Python converts the decimal numeral 0.2 to floating-point. Python does not specify what floating-point format implementations use, but it is most commonly IEEE-754 binary64, called “double precision.”
The closest value representable in binary 64 to 0.2 is 0.200000000000000011102230246251565404236316680908203125.
So 59 // 0.2 divides 59 by 0.200000000000000011102230246251565404236316680908203125. The result before truncation is a little less than 295, so 294 is the correct result.