Add Tutorial about extending/inheriting from compas classes

[yck011522]

Feature Request

As a developer of my own library that inherit from compas class, I want a tutorial showing me how my child class can keep core functionality of the compas class, such as the to_data and from_data functions.

Details

Is your feature request related to a problem? Please describe. This started as a problem when my Tool class try to inherit the RobotModel class. I would like to keep the to_data and from_data functionality in my child class. Turns out it is not as easy as I thought. With help from @beverlylytle we managed to come up with a working template that allow my Tool class to call the super class's data functions. :

from compas.robots import RobotModel


class Tool(RobotModel):
    def __init__(self, name):
        super(Tool, self).__init__(name)
        self.extra = "Foo"

    @property
    def data(self):
        data = super(Tool, self).data
        data.update({'extra': self.extra})
        return data

    @data.setter
    def data(self, data):
        super(Tool, self.__class__).data.fset(self, data)
        self.extra = data['extra']
    def to_data(self):
        return self.data

    @classmethod
    def from_data(cls, data):
        tool = Tool(None)
        tool.data = data
        return tool

if __name__ == "__main__":
    from compas.robots import Joint

    t = Tool("Name")
    t.add_joint("J1", Joint.REVOLUTE , t.add_link("L1"), t.add_link("L2"))
    print (t.data)

    # Test object creation from data
    t2 = Tool.from_data(t.data)
    print (t2.data)

    # Test copy by data assignment
    t3 = Tool(None)
    t3.data = t.data
    print (t3.data)

I believe other people might want to do the same and this template might be of use. I suggesting adding a page in Docs/Tutorials about Inheriting compas classes, that contain a template for doing this and perhaps other best practice suggestions. Hope this helps someone.

Note One of the difficulty is to figure out super().data = data doesn't work and has to be super(Tool, self.__class__).data.fset(self, data) as explained in https://stackoverflow.com/questions/10810369/python-super-and-setting-parent-class-property

[jf---]

@yck011522 has this changed with many classes being based on compas.data.Data?

[yck011522]

When I posted this issue, there wasn't many classes within compas that implemented data. Now that has changed. However I think the issue of how users (not us, developers) implement the data class still deserves a page in tutorial.

Especially because users are very likely to implement custom classes for serialising their own data.

[jf---]

Makes sense, is json serialization invoked automagically in when invoking compas.rpc.Proxy?

[tomvanmele]

serialisation is indeed invoked automatically on all data classes and other JSON serialisable types. the page about implementing data classes is on the to do list: https://compas.dev/compas/latest/devguide/dtypes.html

[jf---]

@yck011522 is this tied to the #681 issue? That is, if serialization works out well incl meshes, then perhaps that inching towards writing URDF's with meshes?

[yck011522]

@jf--- this is not tied to #681 .