Params support for unwatching

[analog-cbarber]

The Params stream class will watch the parameters by default:

        if watch:
            # Subscribe to parameters
            keyfn = lambda x: id(x.owner)
            for _, group in groupby(sorted(parameters, key=keyfn)):
                group = list(group)
                group[0].owner.param.watch(self._watcher, [p.name for p in group])

but it does not save the created Watcher objects returned by the watch method,
so there is no easy way to unwatch them later. So if you are done with the stream but
not the underlying parameters the stream will be kept alive and will continue to get events.

You can work around this by constructing with watch=False and duplicating
the code above, but it would be much nicer if this ability was built into Params
itself.

[petros1999]

Hi there. Μe and my collaborator, would like to work with that issue. As novices to programming we are, we would appreciate any suggestions or guidelines conserning the building of the upper ability into Params, in order to have a more favorable start of our work. Thanks in advance

[analog-cbarber]

I just made a subclass to work around this:

class ParamStream(holoviews.streams.Params):
    """Extends :class:`holoviews.streams.Params` class.

    Specifically provides the ability to unregister parameter watching
    through the :meth:`unwatch` method.
    """

    def __init__(self, parameterized=None, parameters=None, watch=True, watch_only=False, **params):
        super().__init__(
            parameterized = parameterized,
            parameters = parameters,
            watch = False,
            watch_only = False,
            **params
        )

        # Super class does not keep track of watchers, so we have to duplicate code
        # here. See https://github.com/holoviz/holoviews/issues/4360.
        self._watchers = [] # type: List[Watcher]
        if watch:
            # Subscribe to parameters
            keyfn = lambda x: id(x.owner)
            for _, group_iter in groupby(sorted(self.parameters, key=keyfn)):
                group = list(group_iter)
                watcher = group[0].owner.param.watch(self._watcher, [p.name for p in group])
                self._watchers.append(watcher)

    def unwatch(self):
        """Stop watching parameters."""
        for watcher in self._watchers:
            watcher.inst.param.unwatch(watcher)
        self._watchers.clear()

Feel free to copy.

[philippjfr]

We'd very much appreciate a PR adding the unwatch support. Let me know if you need any help contributing. Sadly we don't have a developer guide yet, but you could roughly follow this one: https://panel.holoviz.org/developer_guide/index.html and then replace the develop_install step with this:

doit develop_install -c pyviz/label/dev  -c bokeh -c conda-forge -o unit_tests

[philippjfr]

Thanks for contributing @alexbraditsas!

[github-actions]

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