[Python-Dev] repr(1.1) (original) (raw)

Jewett, Jim J jim.jewett at eds.com
Tue Mar 30 15:26:39 EST 2004

Ka-Ping Yee:

In fact, you've just given a stronger reason for keeping "1.1". Currently, compiling a .py file containing "1.1" produces a .pyc file containing "1.1000000000000001". .pyc files are supposed to be platform-independent. If these files are then run on a platform with different floating-point precision, the .py and the .pyc will produce different results.

In a previous job, every system upgrade meant a C compiler upgrade. We would recompile everything and rerun a week of production data as a regression test. We would get different results. Then I had to find each difference to let the customer decide whether it was large enough to really matter. (It never was.)

I would have been very grateful if I could have flipped a switch to say "Do the math like the old version, even if it was buggy. Do it just this once, so that I can show the customer that any changes are intentional!"

Running a .pyc created on system1 should produce the same results you got on system1, even if system2 could do a better job. Printing a dozen zeros followed by a 1 tells system2 just how precise the calculations should be.

Yes, Decimal would be better for this, but historically it wasn't there.

For that matter, Decimal might be a better default format for 1.1, if a language were starting fresh. It still wouldn't be perfect, though. How many digits should 1.1/3 print?

-jJ

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