Allow Parameterized.param.update to be used as a context manager for temporary updates

[philippjfr]

Implements #685

[maximlt]

I should have chimed in #685 back in February, or maybe at the time it was not so obvious to me, but I think that .param.set and .param.update aren't distinguishable enough naming-wise, that will just cause confusion (constant/readonly kind of confusion comes to mind, since we talked about it recently with Jean-Luc).

How about modifying .param.update so that it can also be used as a context manager? Here's a prototyped implementation where calling .update returns an instance of _Update while previously (as in Param now on the main branch) it returns None. I think that's okay?

class _Update:
    
    def __init__(self, instance):
        self.instance = instance
    
    def __call__(self, **kwargs):
        self.restore = self.instance.kwargs
        self.instance._update(**kwargs)
        return self
    
    def __enter__(self):
        print('ENTER')
    
    def __exit__(self, *exc_details):
        print('EXIT')
        self.instance._update(**self.restore)
        self.restore.clear()


class Parameters:
    
    def __init__(self):
        self.kwargs = dict(a=1)
    
    def update(self, **kwargs):
        return _Update(instance=self)(**kwargs)

    def _update(self, **kwargs):
        self.kwargs = kwargs

If we don't go down that route, we should try to align .set and .update more (i.e. same signatures, work on both classes and instances).

[maximlt]

What do you think about that @philippjfr ?

[philippjfr]

I'll play around with it.

[philippjfr]

Made the changes you requested, ready to review.

[maximlt]

This PR looked good to me overall, I completed it with:

• more tests
• updated docs
• making ParametersRestore private

Thanks!