[Python-Dev] PEP 3101: floats format 'f' and 'F'

[Eric Smith]

Mark Dickinson wrote:
> On Wed, Jul 16, 2008 at 4:15 PM, Eric Smith
> <eric+python-dev at trueblade.com> wrote:
>> There's no exponent until the number gets large.  I haven't looked up how
>> big the number has to get.  On my Mac, it's somewhere between 1e50 and 1e60.
> 
> I think it's around 1e50, courtesy of the rather oddly-phrased line in
> unicodeobject.c
> (this is in py3k) that looks like:
> 
>     if (type == 'f' && (fabs(x) / 1e25) >= 1e25)

I don't know why that test exists.  It comes from Guido in r3417 
(1993-03-16!).  It's from the very first incarnation of formatfloat().

I'd like to remove it, but there's no telling what it would break. 
Surely something written in the last 15+ years depends on it.  But if it 
were removed, then (as Tim points out) only INF and NAN would be in 
uppercase for 'F'.

regrtest.py still works with it removed, except for string_tests.py, 
which is explicitly looking for this behavior, and has this comment:
             # The formatfloat() code in stringobject.c and
             # unicodeobject.c uses a 120 byte buffer and switches from
             # 'f' formatting to 'g' at precision 50, so we expect
             # OverflowErrors for the ranges x < 50 and prec >= 67.

The fixed size buffer could be dealt with, but it doesn't seem worth it 
given the potential breakage.

For now, I'll just make 'F' convert to uppercase, and leave the 1e50 
issue for another release.

Eric.