factorial of negative one (-1)

[Terry Reedy]

On 11/2/2010 6:11 AM, Hrvoje Niksic wrote:

>>>> 1.1 .hex()
> '0x1.199999999999ap+0'
>
> Here it is immediately obvious that the final digit of the infinite
> sequence "1.1999..." is rounded from 9 to a.  Printing the number with
> any more digits would just reveal zeros, as expected.
>
> Does anyone know why Python doesn't accept hex float literals in source
> code?

Assuming that the parser would have no problem with them:
1. the format is relatively recent
2. you can write float.fromhex('<hex literal>')
3. it never occurred to anyone to do so
4. literals are values supplied by the programmer; hex float values are 
rare and when they do occur, they are usually the stored output of a 
previous .hex() in Python or similar in other languages.
5. too easy to confuse in quick reading with normal float literals
6. the format is a bit weird and too esoteric for most programmers; they 
should not be part of the basic syntax that everyone has to learn; 
someone who reads float.fromhex(something) can look it up.

-- 
Terry Jan Reedy