Conversion from fractions.Fraction to bool

[francois-durand]

BPO	39274
Nosy	@rhettinger, @mdickinson, @vstinner, @seberg, @miss-islington, @idomic, @francois-durand
PRs	bpo-39274: Ensure Fraction.__bool__ returns a bool #18017 [3.8] bpo-39274: Ensure Fraction.__bool__() returns a bool (GH-18017) #18376 [3.7] bpo-39274: Ensure Fraction.__bool__() returns a bool (GH-18017) #18377

^{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 = <Date 2020-02-06.14:59:07.888>
created_at = <Date 2020-01-09.12:43:51.476>
labels = ['easy', 'type-bug', '3.9']
title = 'Conversion from fractions.Fraction to bool'
updated_at = <Date 2020-02-06.15:14:42.456>
user = 'https://github.com/francois-durand'

bugs.python.org fields:

activity = <Date 2020-02-06.15:14:42.456>
actor = 'miss-islington'
assignee = 'none'
closed = True
closed_date = <Date 2020-02-06.14:59:07.888>
closer = 'vstinner'
components = []
creation = <Date 2020-01-09.12:43:51.476>
creator = 'francois-durand'
dependencies = []
files = []
hgrepos = []
issue_num = 39274
keywords = ['patch', 'newcomer friendly']
message_count = 12.0
messages = ['359673', '359675', '359677', '359679', '359681', '360077', '361237', '361238', '361488', '361489', '361491', '361492']
nosy_count = 8.0
nosy_names = ['rhettinger', 'mark.dickinson', 'vstinner', 'SilentGhost', 'seberg', 'miss-islington', 'Ido Michael', 'francois-durand']
pr_nums = ['18017', '18376', '18377']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue39274'
versions = ['Python 3.9']

[francois-durand]

As of now, fractions.Fraction.bool is implemented as: return a._numerator != 0. However, this does not necessary return a bool (which would be desired). In particular, when the numerator is a numpy integer, this returns a numpy bool instead. Another solution would be to implement fractions.Fraction.bool as: return bool(numerator). What do you think?

This message follows a thread here: numpy/numpy#15277 .

[mdickinson]

Agreed that bool should return an actual bool.
return bool(a._numerator) does seem like the obvious way to do this.

[mdickinson]

For completeness and to save people going to the NumPy tracker, here's an example of the problem:

Python 3.8.1 (default, Jan  5 2020, 21:32:35) 
[Clang 10.0.1 (clang-1001.0.46.4)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import fractions, numpy
>>> f = fractions.Fraction(numpy.int64(1), 2)
>>> not f
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: __bool__ should return bool, returned numpy.bool_

[vstinner]

return bool(a._numerator) does seem like the obvious way to do this.

Yes, it's a good fix. It's used on other places.

--

numbers.Complex.__bool__() also uses "self != 0". Is it an issue?

[seberg]

Thanks for the quick responses.

@victor Stinner, I suppose you could change numbers.Complex.__bool__() by adding the no-op bool to make it: bool(self != 0).

But I am not sure I feel it is necessary. NumPy is a bit a strange in that it uses its own boolean scalar, and it is easy to override the slot for such objects.

[vstinner]

Does someone want to propose a PR to modify fractions.Fraction.__bool__() to use "return bool(a._numerator)"?

[idomic]

Hi all,

I think this issue can be closed right?
Saw a successful PR.

[SilentGhost]

"Successful" PR would be merged into master. This issue is still in "patch review" stage.

[vstinner]

New changeset 427c84f by Sebastian Berg in branch 'master':
bpo-39274: Ensure Fraction.__bool__() returns a bool (GH-18017)
427c84f

[vstinner]

Thanks Sebastian Berg for the fix, and thanks François Durand for the bug report! This issue is fixed in the master branch, and backports to 3.7 and 3.8 will land soon automatically (once the CI tests pass).

[miss-islington]

New changeset 0d03a10 by Miss Islington (bot) in branch '3.8':
bpo-39274: Ensure Fraction.__bool__() returns a bool (GH-18017)
0d03a10

[miss-islington]

New changeset 705d271 by Miss Islington (bot) in branch '3.7':
bpo-39274: Ensure Fraction.__bool__() returns a bool (GH-18017)
705d271