fractions: Should we support unicode in width/precision formatting fields?

Bug report

Bug description:

Currently, specification allows only [0-9] digits. Though, actual implementation permits unicode symbols for float/Decimal's, but not Fraction's:

>>> f"{decimal.Decimal('123'):.١١f}"  # arabic 11 in precision
'123.00000000000'
>>> f"{fractions.Fraction('123'):.١١f}"
Traceback (most recent call last):
  File "<python-input-9>", line 1, in <module>
    f"{fractions.Fraction('123'):.١١f}"
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/sk/src/cpython/Lib/fractions.py", line 600, in __format__
    raise ValueError(
    ...<2 lines>...
    )
ValueError: Invalid format specifier '.١١f' for object of type 'Fraction'
>>> f"{float(fractions.Fraction('123')):.١١f}"
'123.00000000000'

Quick tests shows no measurable performance penalty with unicode support:

$ python -m timeit -s 'from fractions import Fraction as F' 'format(F(123), ".11f")'
10000 loops, best of 5: 39.2 usec per loop
$ python -m timeit -s 'from fractions import Fraction as F' 'format(F(123), ".١١f")'  # with patch
5000 loops, best of 5: 40.2 usec per loop

diff --git a/Lib/fractions.py b/Lib/fractions.py
index 063f28478c..b4120b2beb 100644
--- a/Lib/fractions.py
+++ b/Lib/fractions.py
@@ -170,7 +170,7 @@ def _round_to_figures(n, d, figures):
     (?P<zeropad>0(?=[0-9]))?
     (?P<minimumwidth>0|[1-9][0-9]*)?
     (?P<thousands_sep>[,_])?
-    (?:\.(?P<precision>0|[1-9][0-9]*))?
+    (?:\.(?P<precision>0|\d*))?
     (?P<presentation_type>[eEfFgG%])
 """, re.DOTALL | re.VERBOSE).fullmatch

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-140654

Examinez d’abord l’expression régulière de spécification de format dans Lib/fractions.py et la PR liée gh-140654. Reproduisez les exemples de précision avec des chiffres arabes pour Fraction, Decimal et float, puis comparez le résultat avec la spécification de format documentée. Le travail est terminé lorsque Fraction accepte de manière cohérente la syntaxe de précision Unicode prévue.