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bpo-45995: add "z" format specifer to coerce negative 0 to zero #30049

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Merged
mdickinson merged 25 commits into from
Apr 11, 2022
Merged

bpo-45995: add "z" format specifer to coerce negative 0 to zero #30049

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a633e88
bpo-45995: add "z" format specifer to coerce negative 0 to zero
belm0 Dec 7, 2021
636da05
formatting
belm0 Dec 11, 2021
3f4085d
implementation for Decimal
belm0 Dec 13, 2021
68a049e
📜🤖 Added by blurb_it.
blurb-it[bot] Dec 14, 2021
ad32be5
consistent flag names
belm0 Dec 14, 2021
3dcaf5f
add test case for integer value with z option
belm0 Feb 3, 2022
6b9ab3b
reference pending PEP
belm0 Feb 4, 2022
e243568
Apply some formatting and doc suggestions
belm0 Mar 16, 2022
be4fda2
revise "z" option description
belm0 Mar 19, 2022
043d76a
add test cases for explicit sign option
belm0 Mar 19, 2022
104e023
revise tests for format options expected to fail on floats
belm0 Mar 19, 2022
61c64df
"float presentation" -> "floating-point presentation"
belm0 Mar 19, 2022
76d61ae
news file terminating newline
belm0 Mar 19, 2022
33fe72c
add test coverage for Decimal bugs
belm0 Mar 19, 2022
9393136
Decimal: handle 'z' fill character correctly
belm0 Mar 21, 2022
f88f7fc
Decimal: const qualifier on fmt variable
belm0 Mar 21, 2022
20c9cf1
fix rounding of 'e', 'g', and '%' presentation types for Decimal
belm0 Mar 23, 2022
bf1a891
fix Decimal directed rounding
belm0 Mar 23, 2022
3f5b392
consistency among tests
belm0 Mar 23, 2022
8d7a745
fix stack-use-after-scope sanitizer error
belm0 Mar 23, 2022
2a24e61
clarify Decimal strategy
belm0 Mar 23, 2022
0cbff6a
fix Decimal format parsing
belm0 Apr 6, 2022
8e7b51c
fix Decimal when no precision is specified
belm0 Apr 7, 2022
418ab76
fix comment typo
belm0 Apr 7, 2022
3ee6f6b
add attribution to news blurb
belm0 Apr 11, 2022
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clarify Decimal strategy
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@belm0
belm0 committed Mar 23, 2022
commit 2a24e610d1384608b43050121d22b412cc9f8355
4 changes: 1 addition & 3 deletions Modules/_decimal/_decimal.c
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Expand Up @@ -3360,9 +3360,7 @@ dec_format(PyObject *dec, PyObject *args)
if (no_neg_0 && mpd_isnegative(mpd) && !mpd_isspecial(mpd)) {
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/* Round into a temporary (carefully mirroring the rounding
of mpd_qformat_spec()), and check if the result is negative zero.
If so, clear the sign and format this pre-rounded value.
(The format will then do no additional rounding, which is
significant for directed rounding cases like ROUND_CEILING.) */
If so, clear the sign and format the resulting positive zero. */
Comment on lines +3389 to +3392

@belm0 belm0 Mar 23, 2022

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An insight I had recently was that, once negative zero is confirmed somehow, producing the correct output is only a matter of formatting positive zero (which cannot be affected by directed rounding, etc.).

As for how to detect negative zero, the options are: 1) round independently of the format function, or 2) analyze the string result of the format function (as Mark suggested). I found the former easier to manage, since it's a matter of duplicating a small amount of proven mpd library code, and is relatively straightforward to test. In contrast, analyzing the format output involves writing a new and perfectly-correct regex or parser, and imagining all the format spec edge cases to test it with.

mpd_ssize_t prec;
mpd_qcopy(&tmp, mpd, &status);
switch (spec.type) {
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