Re: [Python-ideas] Runtime types vs static types

On 7/2/2017 7:57 AM, Steven D'Aprano wrote:

On Sun, Jul 02, 2017 at 09:38:11PM +1000, Chris Angelico wrote:

...

On Sun, Jul 2, 2017 at 9:16 PM, Steven D'Aprano wrote:

...

If we want to support that optimization, we could add an optimization flag that strips annotations at runtime, just as the -OO flag strips docstrings. That becomes a matter of *consenting adults* -- if you don't want annotations, you don't need to keep them, but it then becomes your responsibility that you don't try to use them. (If you do, you'll get a runtime AttributeError.)

IMO people should act as if this will eventually be the case. Annotations should be evaluated solely for the purpose of populating __annotations__, and not for any sort of side effects - just like with assertions.

Avoiding side-effects is generally a good idea, but I think that's probably taking it too far.

I think that we should assume that

def func(x:Spam()): ...

will always look up and call Spam when the function is defined. But we should be prepared that

func.__annotations__

might not exist, if we're running in a highly-optimized mode, or MicroPython, or similar.

Code that does not control the compilation of the file with func should also not assume the existence of func.__doc__. On the other hand, programs, such as IDEs, that do control compilation, by calling the standard compile(), can assume both attributes if they pass the appropriate compile flags. -- Terry Jan Reedy