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Commitf8d56b9

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mdickinsonserhiy-storchaka
authored andcommitted
pythongh-67790: Support basic formatting for Fraction (python#111320)
PRpython#100161 added fancy float-style formatting for the Fraction type,but left us in a state where basic formatting for fractions (alignment,fill, minimum width, thousands separators) still wasn't supported.This PR adds that support.---------Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
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‎Doc/library/fractions.rst‎

Lines changed: 30 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -106,6 +106,10 @@ another rational number, or from a string.
106106
presentation types ``"e"``, ``"E"``, ``"f"``, ``"F"``, ``"g"``, ``"G"``
107107
and ``"%""``.
108108

109+
..versionchanged::3.13
110+
Formatting of:class:`Fraction` instances without a presentation type
111+
now supports fill, alignment, sign handling, minimum width and grouping.
112+
109113
..attribute::numerator
110114

111115
Numerator of the Fraction in lowest term.
@@ -201,17 +205,36 @@ another rational number, or from a string.
201205

202206
..method::__format__(format_spec, /)
203207

204-
Provides support for float-style formatting of:class:`Fraction`
205-
instances via the:meth:`str.format` method, the:func:`format` built-in
206-
function, or:ref:`Formatted string literals<f-strings>`. The
207-
presentation types ``"e"``, ``"E"``, ``"f"``, ``"F"``, ``"g"``, ``"G"``
208-
and ``"%"`` are supported. For these presentation types, formatting for a
209-
:class:`Fraction` object ``x`` follows the rules outlined for
210-
the:class:`float` type in the:ref:`formatspec` section.
208+
Provides support for formatting of:class:`Fraction` instances via the
209+
:meth:`str.format` method, the:func:`format` built-in function, or
210+
:ref:`Formatted string literals<f-strings>`.
211+
212+
If the ``format_spec`` format specification string does not end with one
213+
of the presentation types ``'e'``, ``'E'``, ``'f'``, ``'F'``, ``'g'``,
214+
``'G'`` or ``'%'`` then formatting follows the general rules for fill,
215+
alignment, sign handling, minimum width, and grouping as described in the
216+
:ref:`format specification mini-language<formatspec>`. The "alternate
217+
form" flag ``'#'`` is supported: if present, it forces the output string
218+
to always include an explicit denominator, even when the value being
219+
formatted is an exact integer. The zero-fill flag ``'0'`` is not
220+
supported.
221+
222+
If the ``format_spec`` format specification string ends with one of
223+
the presentation types ``'e'``, ``'E'``, ``'f'``, ``'F'``, ``'g'``,
224+
``'G'`` or ``'%'`` then formatting follows the rules outlined for the
225+
:class:`float` type in the:ref:`formatspec` section.
211226

212227
Here are some examples::
213228

214229
>>> from fractions import Fraction
230+
>>> format(Fraction(103993, 33102), '_')
231+
'103_993/33_102'
232+
>>> format(Fraction(1, 7), '.^+10')
233+
'...+1/7...'
234+
>>> format(Fraction(3, 1), '')
235+
'3'
236+
>>> format(Fraction(3, 1), '#')
237+
'3/1'
215238
>>> format(Fraction(1, 7), '.40g')
216239
'0.1428571428571428571428571428571428571429'
217240
>>> format(Fraction('1234567.855'), '_.2f')

‎Doc/whatsnew/3.13.rst‎

Lines changed: 8 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -212,6 +212,14 @@ email
212212
(Contributed by Thomas Dwyer and Victor Stinner for:gh:`102988` to improve
213213
the CVE-2023-27043 fix.)
214214

215+
fractions
216+
---------
217+
218+
* Formatting for objects of type:class:`fractions.Fraction` now supports
219+
the standard format specification mini-language rules for fill, alignment,
220+
sign handling, minimum width and grouping. (Contributed by Mark Dickinson
221+
in:gh:`111320`)
222+
215223
glob
216224
----
217225

‎Lib/fractions.py‎

Lines changed: 68 additions & 19 deletions
Original file line numberDiff line numberDiff line change
@@ -139,6 +139,23 @@ def _round_to_figures(n, d, figures):
139139
returnsign,significand,exponent
140140

141141

142+
# Pattern for matching non-float-style format specifications.
143+
_GENERAL_FORMAT_SPECIFICATION_MATCHER=re.compile(r"""
144+
(?:
145+
(?P<fill>.)?
146+
(?P<align>[<>=^])
147+
)?
148+
(?P<sign>[-+ ]?)
149+
# Alt flag forces a slash and denominator in the output, even for
150+
# integer-valued Fraction objects.
151+
(?P<alt>\#)?
152+
# We don't implement the zeropad flag since there's no single obvious way
153+
# to interpret it.
154+
(?P<minimumwidth>0|[1-9][0-9]*)?
155+
(?P<thousands_sep>[,_])?
156+
""",re.DOTALL|re.VERBOSE).fullmatch
157+
158+
142159
# Pattern for matching float-style format specifications;
143160
# supports 'e', 'E', 'f', 'F', 'g', 'G' and '%' presentation types.
144161
_FLOAT_FORMAT_SPECIFICATION_MATCHER=re.compile(r"""
@@ -414,27 +431,42 @@ def __str__(self):
414431
else:
415432
return'%s/%s'% (self._numerator,self._denominator)
416433

417-
def__format__(self,format_spec,/):
418-
"""Format this fraction according to the given format specification."""
419-
420-
# Backwards compatiblility with existing formatting.
421-
ifnotformat_spec:
422-
returnstr(self)
434+
def_format_general(self,match):
435+
"""Helper method for __format__.
423436
437+
Handles fill, alignment, signs, and thousands separators in the
438+
case of no presentation type.
439+
"""
424440
# Validate and parse the format specifier.
425-
match=_FLOAT_FORMAT_SPECIFICATION_MATCHER(format_spec)
426-
ifmatchisNone:
427-
raiseValueError(
428-
f"Invalid format specifier{format_spec!r} "
429-
f"for object of type{type(self).__name__!r}"
430-
)
431-
elifmatch["align"]isnotNoneandmatch["zeropad"]isnotNone:
432-
# Avoid the temptation to guess.
433-
raiseValueError(
434-
f"Invalid format specifier{format_spec!r} "
435-
f"for object of type{type(self).__name__!r}; "
436-
"can't use explicit alignment when zero-padding"
437-
)
441+
fill=match["fill"]or" "
442+
align=match["align"]or">"
443+
pos_sign=""ifmatch["sign"]=="-"elsematch["sign"]
444+
alternate_form=bool(match["alt"])
445+
minimumwidth=int(match["minimumwidth"]or"0")
446+
thousands_sep=match["thousands_sep"]or''
447+
448+
# Determine the body and sign representation.
449+
n,d=self._numerator,self._denominator
450+
ifd>1oralternate_form:
451+
body=f"{abs(n):{thousands_sep}}/{d:{thousands_sep}}"
452+
else:
453+
body=f"{abs(n):{thousands_sep}}"
454+
sign='-'ifn<0elsepos_sign
455+
456+
# Pad with fill character if necessary and return.
457+
padding=fill* (minimumwidth-len(sign)-len(body))
458+
ifalign==">":
459+
returnpadding+sign+body
460+
elifalign=="<":
461+
returnsign+body+padding
462+
elifalign=="^":
463+
half=len(padding)//2
464+
returnpadding[:half]+sign+body+padding[half:]
465+
else:# align == "="
466+
returnsign+padding+body
467+
468+
def_format_float_style(self,match):
469+
"""Helper method for __format__; handles float presentation types."""
438470
fill=match["fill"]or" "
439471
align=match["align"]or">"
440472
pos_sign=""ifmatch["sign"]=="-"elsematch["sign"]
@@ -530,6 +562,23 @@ def __format__(self, format_spec, /):
530562
else:# align == "="
531563
returnsign+padding+body
532564

565+
def__format__(self,format_spec,/):
566+
"""Format this fraction according to the given format specification."""
567+
568+
ifmatch:=_GENERAL_FORMAT_SPECIFICATION_MATCHER(format_spec):
569+
returnself._format_general(match)
570+
571+
ifmatch:=_FLOAT_FORMAT_SPECIFICATION_MATCHER(format_spec):
572+
# Refuse the temptation to guess if both alignment _and_
573+
# zero padding are specified.
574+
ifmatch["align"]isNoneormatch["zeropad"]isNone:
575+
returnself._format_float_style(match)
576+
577+
raiseValueError(
578+
f"Invalid format specifier{format_spec!r} "
579+
f"for object of type{type(self).__name__!r}"
580+
)
581+
533582
def_operator_fallbacks(monomorphic_operator,fallback_operator):
534583
"""Generates forward and reverse operators given a purely-rational
535584
operator and a function from the operator module.

‎Lib/test/test_fractions.py‎

Lines changed: 47 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -849,12 +849,50 @@ def denominator(self):
849849
self.assertEqual(type(f.denominator),myint)
850850

851851
deftest_format_no_presentation_type(self):
852-
# Triples (fraction, specification, expected_result)
852+
# Triples (fraction, specification, expected_result).
853853
testcases= [
854-
(F(1,3),'','1/3'),
855-
(F(-1,3),'','-1/3'),
856-
(F(3),'','3'),
857-
(F(-3),'','-3'),
854+
# Explicit sign handling
855+
(F(2,3),'+','+2/3'),
856+
(F(-2,3),'+','-2/3'),
857+
(F(3),'+','+3'),
858+
(F(-3),'+','-3'),
859+
(F(2,3),' ',' 2/3'),
860+
(F(-2,3),' ','-2/3'),
861+
(F(3),' ',' 3'),
862+
(F(-3),' ','-3'),
863+
(F(2,3),'-','2/3'),
864+
(F(-2,3),'-','-2/3'),
865+
(F(3),'-','3'),
866+
(F(-3),'-','-3'),
867+
# Padding
868+
(F(0),'5',' 0'),
869+
(F(2,3),'5',' 2/3'),
870+
(F(-2,3),'5',' -2/3'),
871+
(F(2,3),'0','2/3'),
872+
(F(2,3),'1','2/3'),
873+
(F(2,3),'2','2/3'),
874+
# Alignment
875+
(F(2,3),'<5','2/3 '),
876+
(F(2,3),'>5',' 2/3'),
877+
(F(2,3),'^5',' 2/3 '),
878+
(F(2,3),'=5',' 2/3'),
879+
(F(-2,3),'<5','-2/3 '),
880+
(F(-2,3),'>5',' -2/3'),
881+
(F(-2,3),'^5','-2/3 '),
882+
(F(-2,3),'=5','- 2/3'),
883+
# Fill
884+
(F(2,3),'X>5','XX2/3'),
885+
(F(-2,3),'.<5','-2/3.'),
886+
(F(-2,3),'\n^6','\n-2/3\n'),
887+
# Thousands separators
888+
(F(1234,5679),',','1,234/5,679'),
889+
(F(-1234,5679),'_','-1_234/5_679'),
890+
(F(1234567),'_','1_234_567'),
891+
(F(-1234567),',','-1,234,567'),
892+
# Alternate form forces a slash in the output
893+
(F(123),'#','123/1'),
894+
(F(-123),'#','-123/1'),
895+
(F(0),'#','0/1'),
858896
]
859897
forfraction,spec,expectedintestcases:
860898
withself.subTest(fraction=fraction,spec=spec):
@@ -1218,6 +1256,10 @@ def test_invalid_formats(self):
12181256
'.%',
12191257
# Z instead of z for negative zero suppression
12201258
'Z.2f'
1259+
# z flag not supported for general formatting
1260+
'z',
1261+
# zero padding not supported for general formatting
1262+
'05',
12211263
]
12221264
forspecininvalid_specs:
12231265
withself.subTest(spec=spec):
Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,2 @@
1+
Implement basic formatting support (minimum width, alignment, fill) for
2+
:class:`fractions.Fraction`.

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