[3.14] gh-87790: support thousands separators for formatting fractional part of Fraction (GH-132204)

Lib/fractions.py

@@ -170,7 +170,11 @@ def _round_to_figures(n, d, figures):
  (?P<zeropad>0(?=[0-9]))?
  (?P<minimumwidth>[0-9]+)?
  (?P<thousands_sep>[,_])?
- (?:\.(?P<precision>[0-9]+))?
+ (?:\.
+ (?=[,_0-9]) # lookahead for digit or separator
+ (?P<precision>[0-9]+)?
+ (?P<frac_separators>[,_])?
+ )?
  (?P<presentation_type>[eEfFgG%])
 """, re.DOTALL | re.VERBOSE).fullmatch
 
@@ -499,6 +503,7 @@ def _format_float_style(self, match):
  minimumwidth = int(match["minimumwidth"] or "0")
  thousands_sep = match["thousands_sep"]
  precision = int(match["precision"] or "6")
+ frac_sep = match["frac_separators"] or ""
  presentation_type = match["presentation_type"]
  trim_zeros = presentation_type in "gG" and not alternate_form
  trim_point = not alternate_form
@@ -555,6 +560,9 @@ def _format_float_style(self, match):
  if trim_zeros:
  frac_part = frac_part.rstrip("0")
  separator = "" if trim_point and not frac_part else "."
+ if frac_sep:
+ frac_part = frac_sep.join(frac_part[pos:pos + 3]
+ for pos in range(0, len(frac_part), 3))
  trailing = separator + frac_part + suffix
 
  # Do zero padding if required.

Lib/test/test_fractions.py

@@ -1322,6 +1322,8 @@ def test_format_e_presentation_type(self):
  # Thousands separators
  (F('1234567.123456'), ',.5e', '1.23457e+06'),
  (F('123.123456'), '012_.2e', '0_001.23e+02'),
+ # Thousands separators for fractional part (or for integral too)
+ (F('1234567.123456'), '.5_e', '1.234_57e+06'),
  # z flag is legal, but never makes a difference to the output
  (F(-1, 7**100), 'z.6e', '-3.091690e-85'),
  ]
@@ -1447,6 +1449,12 @@ def test_format_f_presentation_type(self):
  (F('1234567'), ',.2f', '1,234,567.00'),
  (F('12345678'), ',.2f', '12,345,678.00'),
  (F('12345678'), ',f', '12,345,678.000000'),
+ # Thousands separators for fractional part (or for integral too)
+ (F('123456.789123123'), '._f', '123456.789_123'),
+ (F('123456.789123123'), '.7_f', '123456.789_123_1'),
+ (F('123456.789123123'), '.9_f', '123456.789_123_123'),
+ (F('123456.789123123'), '.,f', '123456.789,123'),
+ (F('123456.789123123'), '_.,f', '123_456.789,123'),
  # Underscore as thousands separator
  (F(2, 3), '_.2f', '0.67'),
  (F(2, 3), '_.7f', '0.6666667'),
@@ -1620,6 +1628,11 @@ def test_invalid_formats(self):
  '.f',
  '.g',
  '.%',
+ # Thousands separators before precision
+ '._6e',
+ '._6f',
+ '._6g',
+ '._6%',
  # Z instead of z for negative zero suppression
  'Z.2f'
  # z flag not supported for general formatting

Misc/NEWS.d/next/Library/2025-04-07-10-20-16.gh-issue-87790.X2SjJe.rst

@@ -0,0 +1,2 @@
+Support underscore and comma as thousands separators in the fractional part
+for :class:`~fractions.Fraction`'s formatting. Patch by Sergey B Kirpichev.