[Python-Dev] Status of PEP 484 and the typing module (original) (raw)

Guido van Rossum guido at python.org
Fri May 22 19:32:37 CEST 2015

On Fri, May 22, 2015 at 10:23 AM, Jim J. Jewett <jimjjewett at gmail.com> wrote:

At Thu May 21 22:27:50 CEST 2015, Guido wrote: > I want to encourage users to think about annotations as types, > and for most users the distinction between type and class is > too subtle, So what is the distinction that you are trying to make? That a type refers to a variable (name), and a class refers to a piece of data (object) that might be bound to that name?

Sort of. But really a type is something in the mind of the type checker (or the programmer) while the class is a concept that can be inspected at runtime.

Whatever the intended distinction is, please be explicit in the PEP, even if you decide to paper it over in normal code. For example, the above distinction would help to explain why the typing types can't be directly instantiated, since they aren't meant to refer to specific data. (They can still be used as superclasses because practicality beats purity, and using them as a marker base class is practical.)

There will have to be documentation and tutorials beyond the PEP. The PEP mostly defines a standard to be used by people implementing type checkers.

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