> Python really needs to take the Typescript approach of "all valid Python4 is valid Python3"
It is called type hints, and is already there. TS typing doesn't bring any perf benefits over plain JS.
You really need dedicated types for `int64` and something like `final`. Consider:
class Foo:
__slots__ = ("a", "b")
a: int
b: float
* a user can define subtype `class my_int(int)`, so you cannot optimize the layout of `class Foo`
* the builtin `int` and `float` are big-int like numbers, so operations on them are branchy and allocating.
and the fact that Foo is mutable and that `id(foo.a)` has to produce something complicates things further.
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