Instance methods of subclass are recognized as "class methods"

[ds1sqe]

If there is a rust struct like below,

use pyo3::{exceptions::PyValueError, prelude::*, types::PyDict};

#[pyclass(subclass)]
pub struct Animal {}

#[pymethods]
impl Animal {
    #[new]
    pub fn new() -> PyResult<Self> {
        Err(PyValueError::new_err("not_implemented"))
    }
    /// Configure with given config.
    pub fn configure(&mut self, valid_config: &Bound<'_, PyDict>) -> PyResult<()> {
        Err(PyValueError::new_err("not_implemented"))
    }

    pub fn run(&self) -> PyResult<()> {
        Err(PyValueError::new_err("not_implemented"))
    }
}

#[pymodule]
mod ex {
    #[pymodule_export]
    use super::Animal;
}

and then at python, inherit like below,

import ex
from ex import Animal


class Dog(Animal):
    def __new__(cls):
        return cls

    def configure(self, valid_config):
        self.cfg = valid_config

    def run(self):
        print(repr(self.cfg))

This (use as class method) works. ( output : {'name': 'foo bar'} )

config = dict({"name": "foo bar"})
dog = Dog()
Dog.configure(dog, config)
Dog.run(dog)

But if i use this as a instance method, like

config = dict({"name": "foo bar"})
dog = Dog()
dog.configure(config)
dog.run()

The Error Occurs.

    dog.configure(config)
    ~~~~~~~~~~~~~^^^^^^^^
TypeError: Dog.configure() missing 1 required positional argument: 'valid_config'

Is there are solution for solve this? I want to use instance method

ps: this works too.

dog = Dog()
dog.configure(dog, config)
dog.run(dog)

[Icxolu]

The problem here is your Dog.__new__ implementation. It is supposed to return a new instance of the class, but you are returning the class object itself:

>>> type(Dog())
type # should be "Dog"

So your dog is not an instance of Dog (but of type), that's why the instance syntax is not working. I believe the class method syntax works here, because it does not validate what self is. It could be any unrelated type for that matter:

class A:
    ...

class Dog:
    def configure(self, valid_config):
        self.cfg = valid_config

>>> a = A()
>>> Dog.configure(a, {})
>>> a.cfg
{}

This pure Python example works without problem (but pretty cursed I guess)

[ds1sqe]

Is there are any ways to return a instance of dog?

I want to use python as a plugin for a rust based program,

Rust expose a base python classes
-> Python implement and extend those
--> Load a python plugins at Rust

[ds1sqe]

This works!!

use pyo3::{exceptions::PyValueError, prelude::*, types::PyDict};

#[pyclass(subclass)]
pub struct Animal {}

#[pymethods]
impl Animal {
    #[new]
    pub fn new() -> PyResult<Self> {
        println!("Animal::new");
        Ok(Self {})
    }
    /// Configure with given config.
    pub fn configure(&mut self, valid_config: &Bound<'_, PyDict>) -> PyResult<()> {
        Err(PyValueError::new_err("not_implemented"))
    }

    pub fn run(&self) -> PyResult<()> {
        Err(PyValueError::new_err("not_implemented"))
    }
}

#[pymodule]
mod ex {
    #[pymodule_export]
    use super::Animal;
}

import ex
from ex import Animal


class Dog(Animal):
    def __init__(self):
        self.name = "Foo"
        self.kind = "Dog"

    def configure(self, valid_config):
        self.cfg = valid_config

    def run(self):
        print(repr(self.cfg))


def main():
    config = dict({"name": "foo bar"})

    dog = Dog()

    print(dog.name)
    print(dog.kind)

    print(type(dog))

    dog.configure(config)

    dog.run()


if __name__ == "__main__":
    main()

Output:

Animal::new
Foo
Dog
<class '__main__.Dog'>
{'name': 'foo bar'}