On 1/12/21 10:37 PM, Chris Angelico wrote:
On Wed, Jan 13, 2021 at 5:05 PM Steven D'Aprano wrote:
On Wed, Jan 13, 2021 at 04:47:06AM +1100, Chris Angelico wrote:
That'd leave open
the option for "foo() if x else foo()" to be optimized down to just
"foo()", although I don't think that particular one is needed.
That would be an unsafe optimization. Not all objets are representable
as truthy/falsey values
Not even all builtin values. This is in Python 3.9:
>>> bool(NotImplemented)
<stdin>:1: DeprecationWarning: NotImplemented should not be used in
a boolean context
True
I believe that 3.10 makes it an error. If not 3.10, then it will surely
happen soon. But even without the change to NotImplemented, it has never
been the case that *every* object is guaranteed to be either truthy or
falsey. At least not since the Python 1.x `__nonzero__` dunder was put
into the language.
But this is exactly where we started: with a boolification that fails,
in a context where the result wouldn't actually change anything.
Actually calling bool() on something will continue to have the
behaviour you're describing, but if the truthiness or falsiness would
make no difference, is the interpreter required to find out?
Yes.
Optimizations are an implementation detail, and implementation details should
not change the language.
--
~Ethan~
_______________________________________________
Python-Dev mailing list -- python-dev@python.org
To unsubscribe send an email to python-dev-le...@python.org
https://mail.python.org/mailman3/lists/python-dev.python.org/
Message archived at
https://mail.python.org/archives/list/python-dev@python.org/message/JFOAJSXWH5KO32YVBN2LKZCPWAFMG63G/
Code of Conduct: http://python.org/psf/codeofconduct/
