[Python-Dev] repr(1.1)

[Jewett, Jim J]

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