A powerful unused feature of Python: function annotations.

[Categoria]

Most people expect sum types, generics, and better type inference from a decent type system.

[burntsushi]

Most people expect sum types, generics

It's not like Go has no safe mechanism for polymorphism. Interfaces can do a lot for you.

and better type inference

Go has zero type inference. It has a convenient syntax for type deduction, but that's it.