ABCs -> infix syntax for isinstance() ?

[Terry Reedy]

Boris Borcic wrote:
> Given the ABC innovation, maybe an infix syntax for isinstance() would 
> be good.
> 
> Possibilities :
> 
> - stealing "is" away from object identity. As a motivation, true use 
> cases for testing object identity are rare; forcing the usage of a 
> function or method to test it, would dissuade abuse.
> 
> - allowing containment tests, ie "x in Number" to invoke isinstance() in 
> the background when the container is of type <type>. My brain is too 
> muddled by flu at the moment, to see whether Guido's fabled time machine 
> allowed him to already provide all the necessities in py26.
> Any takers ?

I believe this could be done by adding a __contains__ method to type.
(It does not have one now).  Then x in X should work for all classes 
that are instances of type or a subclass thereof.


> - combining both keywords to create a third one, eg "is in"