[Python-ideas] Runtime types vs static types

[Steven D'Aprano]

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 <steve at pearwood.info> 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.


-- 
Steve