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Support .as_integer_ratio() in fractions.Fraction #82017
Description
| BPO | 37836 |
|---|---|
| Nosy | @rhettinger, @mdickinson, @serhiy-storchaka, @jdemeyer |
| PRs |
Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.
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GitHub fields:
assignee = None
closed_at = None
created_at = <Date 2019-08-13.09:41:19.711>
labels = ['library', '3.9']
title = 'Support .as_integer_ratio() in fractions.Fraction'
updated_at = <Date 2022-01-02.22:00:12.998>
user = 'https://github.com/jdemeyer'bugs.python.org fields:
activity = <Date 2022-01-02.22:00:12.998>
actor = 'rhettinger'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2019-08-13.09:41:19.711>
creator = 'jdemeyer'
dependencies = []
files = []
hgrepos = []
issue_num = 37836
keywords = ['patch']
message_count = 6.0
messages = ['349536', '349933', '349940', '349942', '349945', '409531']
nosy_count = 5.0
nosy_names = ['rhettinger', 'mark.dickinson', 'stutzbach', 'serhiy.storchaka', 'jdemeyer']
pr_nums = ['15327', '15328']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue37836'
versions = ['Python 3.9']
Activity
jdemeyer commentedon Aug 13, 2019
Currently, the fractions.Fraction constructor accepts an .as_integer_ratio() method only for the specific types "float" and "Decimal". It would be good to support this for arbitrary classes.
This is part of what was proposed in bpo-37822, but without adding the math.operator() function.
serhiy-storchaka commentedon Aug 19, 2019
I afraid this can slow down the Fraction constructor.
serhiy-storchaka commentedon Aug 19, 2019
See bpo-37884 which uses a C accelerator.
jdemeyer commentedon Aug 19, 2019
Note that that doesn't replace this issue, because I need to support as_integer_ratio both in the *numerator* and *denominator*.
jdemeyer commentedon Aug 19, 2019
No, it doesn't! It even speeds up the constructor in some cases:
./python -m perf timeit --duplicate 200 -s 'from fractions import Fraction; x = 1' 'Fraction(x)'
BEFORE: Mean +- std dev: 826 ns +- 20 ns
AFTER: Mean +- std dev: 814 ns +- 17 ns
./python -m perf timeit --duplicate 200 -s 'from fractions import Fraction; x = 1' 'Fraction(x, x)'
BEFORE: Mean +- std dev: 1.44 us +- 0.03 us
AFTER: Mean +- std dev: 1.46 us +- 0.02 us
./python -m perf timeit --duplicate 200 -s 'from fractions import Fraction; x = Fraction(1)' 'Fraction(x)'
BEFORE: Mean +- std dev: 1.64 us +- 0.03 us
AFTER: Mean +- std dev: 1.30 us +- 0.04 us
./python -m perf timeit --duplicate 200 -s 'from fractions import Fraction; x = Fraction(1)' 'Fraction(x, x)'
BEFORE: Mean +- std dev: 3.03 us +- 0.05 us
AFTER: Mean +- std dev: 2.34 us +- 0.06 us
./python -m perf timeit --duplicate 200 -s 'from fractions import Fraction; x = 1.0' 'Fraction(x)'
BEFORE: Mean +- std dev: 1.82 us +- 0.02 us
AFTER: Mean +- std dev: 1.29 us +- 0.04 us
rhettinger commentedon Jan 2, 2022
I don't think this is a door we should open:
This currently raises a useful exception:
TypeError: both arguments should be Rational instances
That is especially helpful in avoiding cases like this:
>>> Fraction(1.1, 3.3) Fraction(2476979795053773, 7430939385161318)If that output is desired, the two conversions should be explicit.
>>> Fraction(1.1) / Fraction(3.3) Fraction(2476979795053773, 7430939385161318I recommend rejecting this feature request as being more likely to be hazardous than helpful.
serhiy-storchaka commentedon Apr 21, 2022
Concur with @rhettinger.
serhiy-storchaka commentedon Jun 8, 2024
This proposition was rejected because it used
as_integer_ratio()in both single- and two-argument forms of the Fraction constructor. But these two forms have different roles. The former converts a number to a Fraction or parses a string representation of fraction. The latter creates a fraction from two rationals (and this is perhaps too much, it could be limited to integers). Conversion from integer supports not only rational numbers, but alsofloatandDecimal. Supportingas_integer_ratio()here would allow to convertfloat128and other non-rational numbers to Fraction.So I reopen this issue with more limited goal -- supporting
as_integer_ratio()in a single-argument form of the Fraction constructor.pythongh-82017: Support as_integer_ratio() in the Fraction constructor
pfmoore commentedon Jun 8, 2024
Agreed this would be a nice generalisation for the case of converting a user-defined type to a fraction (the user defined type just has to define
as_integer_ratioand thenFraction(value)works as expected). But it should not apply to the 2-argument case.gh-82017: Support as_integer_ratio() in the Fraction constructor (GH-…