Fix typing

[ego-thales]

See below.

[eliegoudout]

Should first ask for help and confirm thaat the way to go is writing a mypy plugin.
https://mypy.readthedocs.io/en/stable/extending_mypy.html

[eliegoudout]

Known issues

from paramclasses import ParamClass, protected


class A(ParamClass):
    x1: int = 0
    x2: int = protected(0)  # Should PASS
    x3: int = protected(None)  # Should FAIL (None)
    x4 = protected(0)

    @protected  # Should PASS
    @property
    def y(self) -> int:
        return self.x1 + self.x2 + self.x4  # Should PASS

    @protected
    def z(self) -> int:
        return self.x1 + self.x2 + self.x4  # Should PASS

    @property
    def t(self) -> int:
        y: int = self.y  # Should PASS
        z: int = self.z()  # Should PASS
        return y + z


A(x1=None)  # Should FAIL (None)
A(0)  # Should FAIL (signature)
A(y=0)  # Should FAIL (signature)
A(x2=0)  # Should FAIL (Final)
a = A()
A.x1 = None  # Should FAIL (None)
a.x1 = None  # Should FAIL (None)
A.x2 = 0  # Should FAIL (Final)
a.x2 = 0  # Should FAIL (Final)
A.x4 = 0  # Should FAIL (Final)
a.x4 = 0  # Should FAIL (Final)
A.y = lambda: 0  # Should FAIL (final)
a.y = lambda: 0  # Should FAIL (final)
A.z = 0  # Should FAIL (final)
a.z = 0  # Should FAIL (final)

$ mypy
mypy\test.py:6: error: Incompatible types in assignment (expression has type "_ProtectedType", variable has type "int")  [assignment]
mypy\test.py:7: error: Incompatible types in assignment (expression has type "_ProtectedType", variable has type "int")  [assignment]
mypy\test.py:10: error: Decorators on top of @property are not supported  [prop-decorator]
mypy\test.py:13: error: Unsupported operand types for + ("int" and "_ProtectedType")  [operator]
mypy\test.py:17: error: Unsupported operand types for + ("int" and "_ProtectedType")  [operator]
mypy\test.py:21: error: "_ProtectedType" not callable  [operator]
mypy\test.py:22: error: "_ProtectedType" not callable  [operator]

[eliegoudout]

Asked on gitter:

Hi everyone! I come here from the Extending mypy using plugins doc page.

I wrote the library paramclasses, which essentially provides the most basic features of dataclasses (with a couple of edge case fixes), coupled with a @protected decorator that robustly protect overrides in subclasses, at runtime:

from paramclasses import ParamClass, protected

class Foo(ParamClass):
    bar: int = 0

    @protected
    def baz(self) -> None:
        print("This method is protected")

>>> del Foo.baz
<traceback>
ProtectedError: 'baz' is protected by 'Foo'
>>> del Foo(bar=1).baz
<traceback>
ProtectedError: 'baz' is protected by 'Foo'
>>> class SubFoo(Foo):
...     def baz(self) -> None:
...         print("Override fails at runtime!")
...
<traceback>
ProtectedError: 'baz' is protected by 'Foo'

The main purpose of this library is to allow devs to distribute "safe" development tools. For example in machine learning, you could provide base classes with standard methods such as fit, which would be protected, then users could easily implement their algorithms without worrying about overriding core mechanics of the library. The code is heavily tested, but still lacks more users for wide adoption readiness.

This library heavily relies on metaclasses and as such, I have trouble making it work smoothly with static type checking. For example, @protected only acts as a flag detected by the metaclass and has no effect on the decorated methods/attributes. But mypy cannot know that.

My questions are:

• Is writing a mypyplugin the right way to go? If so:
• I detailed in this issue the expected behaviour. How can I implement a test suite (in pytest flavor) to check this? This would be especially useful for me as I start exploring the plugin development.
• Is there a standard way to ship this plugin so that mypy automatically fetches this plugin when third party users install paramclasses?

Thanks a lot!

All the best.
Élie.

[eliegoudout]

For plugin testing, look at pytest-mypy-testing, mypy-test or pytest-mypy-plugins. Ressources in general at awesome-python-typing repo.

Also look mypy's .test.

[eliegoudout]

First try initiated, getting closer. See python/mypy#19481.