[3.14] gh-130662: Accept leading zeros in precision/width for Fraction's formatting (GH-130663) (#136361)

Co-authored-by: Sergey B Kirpichev <[email protected]>
Co-authored-by: Bénédikt Tran <[email protected]>

Author: 3 people

Lib/fractions.py

@@ -168,9 +168,9 @@ def _round_to_figures(n, d, figures):
     # A '0' that's *not* followed by another digit is parsed as a minimum width
     # rather than a zeropad flag.
     (?P<zeropad>0(?=[0-9]))?
-    (?P<minimumwidth>0|[1-9][0-9]*)?
+    (?P<minimumwidth>[0-9]+)?
     (?P<thousands_sep>[,_])?
-    (?:\.(?P<precision>0|[1-9][0-9]*))?
+    (?:\.(?P<precision>[0-9]+))?
     (?P<presentation_type>[eEfFgG%])
 """, re.DOTALL | re.VERBOSE).fullmatch
 

Lib/test/test_fractions.py

@@ -1515,6 +1515,8 @@ def test_format_f_presentation_type(self):
             (F(51, 1000), '.1f', '0.1'),
             (F(149, 1000), '.1f', '0.1'),
             (F(151, 1000), '.1f', '0.2'),
+            (F(22, 7), '.02f', '3.14'),  # issue gh-130662
+            (F(22, 7), '005.02f', '03.14'),
         ]
         for fraction, spec, expected in testcases:
             with self.subTest(fraction=fraction, spec=spec):
@@ -1613,12 +1615,6 @@ def test_invalid_formats(self):
             '=010%',
             '>00.2f',
             '>00f',
-            # Too many zeros - minimum width should not have leading zeros
-            '006f',
-            # Leading zeros in precision
-            '.010f',
-            '.02f',
-            '.000f',
             # Missing precision
             '.e',
             '.f',

Misc/NEWS.d/next/Library/2025-06-02-14-28-30.gh-issue-130662.EIgIR8.rst

@@ -0,0 +1,3 @@
+Accept leading zeros in precision and width fields for
+:class:`~fractions.Fraction` formatting, for example ``format(Fraction(1,
+3), '.016f')``.