[Python-Dev] Backport new float repr to Python 2.7? (original) (raw)

Eric Smith eric at trueblade.com
Mon Oct 12 21:42:52 CEST 2009

[Tim:]

If you don't consider Windows to be a major platform ;-) Besides that there's just no guessing what the Microsoft double->string routines will produce for the 17th digit, the MS routines always produce 3 digits for the exponent in scientific notation, while AFAIK all other platforms produce 2 digits when 3 aren't necessary. For example, on Windows under Python 2.x:

repr(1e47) '1e+047' repr(1e-47) '9.9999999999999997e-048' and "everywhere else": repr(1e47) '1e+47' repr(1e-47) '9.9999999999999997e-48'

Not that it's germane to the discussion, but this 3 digit exponent on Windows was fixed in 2.6.

The leading 0 in the Window's exponents is enough to break a naive doctest too -- and repr(x) does produce scientific notation for "almost all" finite doubles. Why people are obsessed with the relative handful of doubles between 1 and 1000 is beyond me ;-)

As doctest's original author, I have no sympathy for users who burn themselves with float output. Of course it's open to question whether I have sympathy for anyone, ever, but that's not the issue here ;-)

I agree, we shouldn't base the decision to change this based on doctests.

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