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: https://github.com/numpy/numpy/issues/15277 .

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

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_

> ``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?

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.

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

Hi all,

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

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

New changeset 427c84f13f7719e6014a21bd1b81efdc02a046fb by Sebastian Berg in branch 'master':
bpo-39274: Ensure Fraction.__bool__() returns a bool (GH-18017)
https://github.com/python/cpython/commit/427c84f13f7719e6014a21bd1b81efdc02a046fb

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).

New changeset 0d03a1028200646479ef9bb0ad8973d0e73f9525 by Miss Islington (bot) in branch '3.8':
bpo-39274: Ensure Fraction.__bool__() returns a bool (GH-18017)
https://github.com/python/cpython/commit/0d03a1028200646479ef9bb0ad8973d0e73f9525

New changeset 705d271d553b77fd170d27ab8d0f11f638c7f145 by Miss Islington (bot) in branch '3.7':
bpo-39274: Ensure Fraction.__bool__() returns a bool (GH-18017)
https://github.com/python/cpython/commit/705d271d553b77fd170d27ab8d0f11f638c7f145