Using context in a custom script to display deeper additional information

[quique]

My script generates a web form.
I would like to customize the rendering of the elements in the dropdown menu for an ObjectVar, displaying addtional information.

The description context variable allows to use an attribute as a description.
The model FrontPort has an attribute cable, which I'd like to use.
However, this attribute is not a String, but an object (Cable), and apparently the current implementation doesn't use its __str__() method, as it just displays object Object under the frontport name.
I have tried using cable__label and cable.label, but it didn't work.

frontport = ObjectVar(
    model=FrontPort,
    label='Front port',
    context={
        'description': 'cable.label',  # FIXME
    },
)

How can I achieve this?