Is it still necessary to prohibit generics at runtime?

[ilevkivskyi]

There is a paragraph in PEP 484:

You cannot use the subscripted class (e.g. ``Node[int]``) directly in
an expression -- you must define a type alias.  (This restriction
exists because creating the subscripted class, e.g. ``Node[int]``, is
an expensive operation -- usually many times as expensive as
constructing an instance of it.  Using a type alias is also more
readable.)

However, __getitem__ is cached for generics now and this leads to significant speedup (Guido reported up to 300x speedup in extreme cases). I think the above restriction is not necessary anymore and could be removed from the PEP.

[gvanrossum]

However mypy still prohibits it. I'd much rather remove this from mypy and leave it in the PEP than the other way around. ;-)