python/typing

PEP 484, mypy, typeshed, pytype, pyre and typing in PyCharm

Ivan Levkivskyi

@ilevkivskyi

IMO this may be tricky to fix (although doesn't require new features), it is just a tricky/old part of mypy

SaschaSchlemmer

@SaschaSchlemmer

any chance that there is a core dev that would really like to dig his/her teeth into this kind of issue? I know this is probably quite low priority since it is so obscure a usecase.

Ivan Levkivskyi

@ilevkivskyi

It is actually high priority because it appears in really many such obscure cases. However most people are on vacations, so there is no chance this gets fixed before September (October is more realistic)

SaschaSchlemmer

@SaschaSchlemmer

That's encouraging! I really like the direction mypy/python is moving and proper support for typed generics and higher order functions is a big one for being a functional-ish/ multiparadigm language

Christopher Sabater Cordero

@cs-cordero

Hello, is this a bug?

class Base(ABC):
    @property
    @abstractmethod
    def whatever(self) -> str:
        raise NotImplementedError

    @classmethod
    def custom_instantiator(cls: Type[T]) -> T:
        instance = cls()
        ...
        return instance

class Sub(Base):
    pass

Sub()  # error: Cannot instantiate abstract class 'Sub' with abstract attribute 'whatever'
Sub.custom_instantiator()  # no error

i would expect that there would be an error when using custom_instantiator.

Joshua Oreman

@oremanj

@cs-cordero AIUI, mypy assumes that when you use the cls: Type[T] pattern, cls refers to something that can be instantiated, because that's a very common use case and it's not clear how such a constraint could be represented explicitly

And mypy doesn't do interprocedural analysis, so it can't consider whether specifically calling Sub.custom_instantiator() is valid, only whether the definition of custom_instantiator() is valid in isolation

Aritra Biswas

@pandalearnstocode

Hi. Can we use mypy with numba typed list ? Is it possible to use mypy for numpy data types?

Ivan Levkivskyi

@ilevkivskyi

Currently numeric stack is not very well supported, there are some experimental type stubs in numpy-stubs project. You still can use mypy, but it is unlikely it will catch any bugs. We are going to work on adding a better support at some point soon.

Michael Joseph Rosenthal

@micimize

So, I've made some progress on my dynamic class generation by hacking parse, but I'm at a loss as to how I should go about adding generated attributes to class_def.info https://github.com/micimize/datapackage-attrs/blob/master/datapackage_attrs/mypy_plugin.py

Ivan Levkivskyi

@ilevkivskyi

You add them to the symbol table, you can look at mypy.plugins.common.add_method() for an example

Michael Joseph Rosenthal

@micimize

@ilevkivskyi thanks - would I be able to add raw AssignmentStmts for attributes?

Ivan Levkivskyi

@ilevkivskyi

You need to add a Var

Michael Joseph Rosenthal

@micimize

@ilevkivskyi thanks! I think I'm a lot closer now, but probably need to rework the original attrs plugin instead of constructing fake context

Anvar Umarov

@arpanetus

@ilevkivskyi May I ask you a question?

Ivan Levkivskyi

@ilevkivskyi

Yes, go ahead.

Anvar Umarov

@arpanetus

if my python project is not pythonic in the structure, how to tell mypy that the importing file belongs to the project itself?

Ivan Levkivskyi

@ilevkivskyi

I am not sure what exactly you mean, you can just put list of files/directories when running mypy.

If really needed you can use MYPYPATH

Anvar Umarov

@arpanetus

currently i'm running mypy sicp_bot/db/manager.py with a mypy.ini file configured in the root directory of the project

Ivan Levkivskyi

@ilevkivskyi

Have you read the docs at https://mypy.readthedocs.io/en/latest/running_mypy.html?

Anvar Umarov

@arpanetus

sorry for misreading :~) I've set the PYTHONPATH variable and everything works fine now

rpgoldman

@rpgoldman

I have been making a typed subclass of UserDict, and getting an odd error. First, I use this as the header -- is this right:
class _ExtendableTrace(UserDict, Dict[str, np.ndarray]):
When I do that, I get errors from mypy as follows:

posterior_predictive.py:135: error: Definition of "fromkeys" in base class "UserDict" is incompatible with definition in base class "dict"
posterior_predictive.py:135: error: Definition of "copy" in base class "UserDict" is incompatible with definition in base class "dict"

Ivan Levkivskyi

@ilevkivskyi

UserDict is already generic in typeshed, so you can just use https://mypy.readthedocs.io/en/latest/common_issues.html#using-classes-that-are-generic-in-stubs-but-not-at-runtime

rpgoldman

@rpgoldman

@ilevkivskyi Thanks! Yes, that works!

Louis Opter

@lopter

Hello, I am wondering why this is invalid:

from typing import List

class MyObject:
  List = List["MyObject"]
  my_attr = True

my_list: MyObject.List = []  # mypy says MyObject.List is an invalid type.

Joshua Oreman

@oremanj

You can't scope type aliases like that, unfortunately

Louis Opter

@lopter

It would be so cool though?

Joshua Oreman

@oremanj

The current reality is what it is independent of coolness

Ivan Levkivskyi

@ilevkivskyi

FWIW this works on master

what is the version you are using

Joshua Oreman

@oremanj

Oh cool, was that a new-semanal feature?

Louis Opter

@lopter

whatever is on pypi

Ivan Levkivskyi

@ilevkivskyi

Are you sure? https://mypy-play.net/?gist=ab933663feb6d5d2b21202c3d655ec12&mypy=0.720&python=3.7

(fixed the link)

^^ @lopter

Louis Opter

@lopter

Oh no, my laptop has an older version indeed

Ivan Levkivskyi

@ilevkivskyi

@oremanj I think it was supported before to some extent

Louis Opter

@lopter

That's awesome

Gareth T

@garetht

is there a way during or after typechecking to iterate through an AST containing mypy's inferred types for every expression (as if reveal_type were placed in the appropriate places)?

Ivan Levkivskyi

@ilevkivskyi

There is no easy way to do this (no public API)

You can find an example of how to do this in mypyc compiler (that still lives in a separate repo for historical reasons)

Gareth T

@garetht

thanks!

Benjamin Kirkbride

@Beefy-Swain

Hey all

Is there a list of big 3rd party projects that have strict type annotations? As in, no any types, all functions annotated, etc

I was wanting to use flask for something, but found that it has a lot of any types

catern

@catern

I have a bunch of mixins which I want to have all take different arguments in their init; is there a way to do this in a type-safe way? it looks like the normal Python way to do it would be with an opaque **kwargs that you just propagate through to super().init, which is not very type-safe

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