Typing module

[dbrgn]

Are there any plans to port the type annotations from the typing module to Micropython?

[dpgeorge]

The MicroPython compiler itself supports type annotations, so in principle the typing module will work. But there are no plans to port it. Feel free to try doing it yourself (you can start just by copying the CPython implementation, like some of the other modules here) and reporting about it here or on https://forum.micropython.org

[dbrgn]

Thanks. Which Python version - if any - does Micropython track?

[dpgeorge]

Which Python version - if any - does Micropython track

As per the README in the top level of the main repo (https://github.com/micropython/micropython/blob/master/README.md) it's Python 3.4 with a bit of extra stuff (eg async/await keywords) from version 3.5.

[dbrgn]

Ah, thanks! I only looked inside the micropython-lib repo :)

So when porting, would it make sense to use the current 3.6 backport directly?

I could probably give it a stab this week. Would be useful to be able to typecheck micropython projects with mypy.

[dpgeorge]

So when porting, would it make sense to use the current 3.6 backport directly?

Yes, because that will likely work and will be more up to date (eg with bug fixes) than earlier versions.

[dbrgn]

I just checked. The module makes a lot of use of the abc module which is not supported yet by micropython (and is probably not that easy to port).

It would probably be best to write dummy classes for all types. That way the typechecking could not be done on Micropython itself, but mypy running on regular python would probably work, with proper stubs.

[pfalcon]

Few comments:

• Writing a module from scratch for micropython-lib is almost always a better choice than to port (CPython stdlib is very bloated).
• If taking from CPython, taking a version from older CPython release (3.3, 3.4) is almost always a better choice, because with each release, modules in CPython become more and more bloated.

[dpgeorge]

If taking from CPython, taking a version from older CPython release (3.3, 3.4) is almost always a better choice,

In this case, typing was introduced in 3.5 and has evolved a lot so 3.6 is probably a better implementation.

[Cediddi]

I saw the micropython-typing module. I can provide a hand. I'm also writing stub files for esp8266 port (1.9.2 currently). I'll release it as soon as I finish machine. Stub files I'm writing are using typing library. It'd be great if micropython would expose a fake typing module. Just to prevent import errors. Two cases are important from typing import something or import typing. I don't think micropython should support from typing import * or give an error to say "you need to install micropython-typing, which would be a minimal typing library.

[stlehmann]

I would really love to have a working typing module for Micropython. Sadly the CPython typing modules makes use of Metaclasses which are not supported by Micropython. I would prefer a lightweight utyping module that allows type-checking with Mypy over a fake module, though.

[stlehmann]

I had a closer look into CPythons typing module and think it would not fit the cause to make a complete port. It is rather complex and makes use of metaclasses which Micropython doesn't support. Also it would take a lot of unnecessary resources as static type-checkers like mypy only exist for CPython at the moment.

I think the workflow for static type-checking Micropython code at the moment looks more like this:

1. add type annotations to the Micropython code
2. Run CPythons mypy for static type-checking
3. Upload the Micropython code to a controller

I think for such use-cases a fake typing module as proposed by @Cediddi would do the job. It allows to import typing classes like Any, Union or the cast() function in Micropython and use them as annotations. The type-checking can be done with mypy using CPythons typing module and its full functionality.

[dbrgn]

@stlehmann yes, I agree (as already suggested in my older comment). Stubs would be sufficient, you don't want to do typechecking on the target platform.

[stlehmann]

I added the fake modules in #297. It works for simple types like Any, Callable. But the generic types like List[int] or Dict[str, int] won' t work. This is because Micropython does not support the __class_getitem__(cls, key) special function that allows the creation of generic class objects. @dpgeorge would it be possible to add that feature?

[jpochyla]

I think a better way would be to avoid running the typing code, rather than shoe-horning a static annotations into the runtime. For now, simple if False: works.