Deprecation of class properties (python>3.11)

[malik-irain]

Same as PyMoDAQ#668

https://github.com/PyMoDAQ/pymodaq_data/blob/5.0.x_dev/src/pymodaq_data/h5modules/exporter.py#L21-L37

FORMAT_DESCRIPTION and FORMAT_EXTENSION are class properties and will be deprecated.

I guess, one could try to implement a metaclass defining them as @abstractmethod and @property

[seb5g]

or just follow this post: https://stackoverflow.com/questions/76249636/class-properties-in-python-3-11

and create our own decorator to implement the same simple getter feature (without everything else a usual property decorator do):

We could implement this in pymodaq_utils and use wherever it is needed...

[malik-irain]

Ok, let me try it, anyways I did it differently in the PR, as what I said wasn't working with the factory

[seb5g]

I just saw it in #50 (comment) do try both and discuss together what we think is simpler and clearer

[malik-irain]

So two methods here:

1. The "replacement" one, where we create our own classproperty decorator (in pymodaq_utils):

class classproperty:
    def __init__(self, func):
        self.fget = func
    def __get__(self, instance, owner):
        return self.fget(owner)

And then the class that needs class properties:

class H5Exporter(metaclass=ABCMeta):
    """Base class for an exporter. """

    # This is to define an abstract class attribute
    @classproperty
    @abstractmethod
    def FORMAT_DESCRIPTION(cls):
        """str: file format description as a short text. eg: text file"""
        raise NotImplementedError

    @classproperty
    @abstractmethod
    def FORMAT_EXTENSION(cls):
        """str: File format extension. eg: txt"""
        raise NotImplementedError

2. Change to simple class attributes

class H5Exporter(metaclass=ABCMeta):
    """Base class for an exporter. """

    FORMAT_EXTENSION: str = NotImplemented
    FORMAT_DESCRIPTION: str = NotImplemented

And then check for presence at the factory level, or later as one wants:

class ExporterFactory:
    exporters_registry = {}
    file_filters = {}
    @classmethod
    def register_exporter(cls) -> Callable:
        def inner_wrapper(wrapped_class) -> Callable:
            if wrapped_class.FORMAT_EXTENSION   is NotImplemented or \
               wrapped_class.FORMAT_DESCRIPTION is NotImplemented:
                raise NotImplementedError(f'{wrapped_class} does not properly provide a valid value for '
                                          f'`FORMAT_EXTENSION` ({wrapped_class.FORMAT_EXTENSION}) or for '
                                          f'`FORMAT_DESCRIPTION` ({wrapped_class.FORMAT_DESCRIPTION})')
            extension = wrapped_class.FORMAT_EXTENSION
            format_desc = wrapped_class.FORMAT_DESCRIPTION
            ...

The first method, is a pure replacement, keeping everything the same but it needs to update pymodaq_utils, then make sure pymodaq_utils is up to date to provides the decorator in the other packages (and that's a little bit annoying).

The second one, is taking a different approach, with just declaring in the abstract class the needed attributes and giving them a value in, the actual implementations . They are never "computed" in the children classes, it's just FORMAT_EXTENSION = 'txt' etc.

For, the splash screen it is different as its property is actually a Singleton. So when PyMoDAQ#610 is solved, Singletons will be available and we could instantiate it as one.

[seb5g]

let's go for the second method!

[seb5g]

done