[Python-Dev] PEP 3101: floats format 'f' and 'F' (original) (raw)

Eric Smith eric+python-dev at trueblade.com
Wed Jul 16 17:15:40 CEST 2008

Mark Dickinson wrote:

On Wed, Jul 16, 2008 at 3:35 PM, Eric Smith <eric+python-dev at trueblade.com> wrote:

Does anyone know why 'F' is the same as 'f'? Wouldn't it make more sense to either drop it, or make it convert the exponent to upper case What exponent? Isn't the point of 'f' formatting that there is no exponent?

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.

$ ./python.exe Python 3.0b1+ (py3k:64984:64985, Jul 15 2008, 20:17:06) [GCC 4.0.1 (Apple Inc. build 5465)] on darwin Type "help", "copyright", "credits" or "license" for more information.

'%f' % 1e100 '1e+100' '%F' % 1e100 '1e+100' '%f' % 1.2 '1.200000'

str.format() works the same.

In C, the only difference seems to be that a NaN or infinity formatted with '%F' is turned into "NAN" or "INF" instead of "nan" or "inf".

Not so in Python.

'%f' % float('nan') 'nan' '%F' % float('nan') 'nan'

But it is the case with 'e':

'%e' % float('nan') 'nan' '%E' % float('nan') 'NAN'

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