Even if you define __bool__() as returning a bool, and error/undefined behavior otherwise, that doesn't eliminate side effects. Is it even possible to nail down a definition to the point that you can say, "Thou shalt not mutate or cause anything" and have it meaningfully enforced in the compiler or interpreter?
-Em On Wed, Jan 13, 2021 at 12:18 AM Paul Sokolovsky <pmis...@gmail.com> wrote: > Hello, > > On Wed, 13 Jan 2021 18:27:07 +1100 > Chris Angelico <ros...@gmail.com> wrote: > > [] > > > > Optimizations are an implementation detail, and implementation > > > details should not change the language. > > > > The language can also be defined in an optimization-friendly way, > > though. Consider how we got positional-only arguments in Python: first > > they existed in C-implemented functions in CPython, even though they > > couldn't exist in pure Python code, and then the functionality got > > added to the language definition, thus permitting the optimization. > > In this case, the culprit seems to be that __bool__() and many other > "special" methods may have side effects. So, just as "const" annotation > would be useful for variables, "pure" (side-effect free) annotation > would be useful for functions. > > But that alone won't help due to too-dynamic nature of Python. It's not > much of an optimization if, at runtime, at each call-site, you need to > check whether a function is pure to decide if you have to call it, or > may skip it. Instead, that rather be done at compile time. > > But checking which method (pure or impure) will be called when is again > complicated statically in Python. What to do about that? Well, we can > introduce, ahem, some "strict" mode, in which *all* __bool__(), > __gt__(), and friends must be declared pure, and for good measure, > returning bool. Then we know we can skip any such method call. > > You see, all heresy starts from small things... > > [] > > -- > Best regards, > Paul mailto:pmis...@gmail.com > _______________________________________________ > 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/4P52JORZ4WBCPC6DERRITDRETEFWT73H/ > Code of Conduct: http://python.org/psf/codeofconduct/ >
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