Subobject dependencies should be dynamic

[philippjfr]

The param.depends decorator supports expressing dependencies on parameters on subobjects. However these dependencies are evaluated only on initialization meaning that if the object is not yet defined then it will error and if it is redefined later it will not set up that dependency. The following example should work but currently errors:

import param

class A(param.Parameterized):
    
    value = param.Parameter()
    
class B(param.Parameterized):
    
    a = param.ObjectSelector()
    
    @param.depends('a.value', watch=True)
    def test_depends(self):
        print(self.a.value)

b = B()
b.a = A()
b.a.value = 1

[jbednar]

I guess whether this is a bug or a requested feature depends on your outlook on life. :-) Seems like you're coming down on the side of "possible feature" given that it wasn't part of the original design, but I agree that it should behave properly in that case, making it also kinda be a bug...

[philippjfr]

Agreed, I clicked on feature request but then almost decided to change the label.

[ceball]

On Thu, May 14, 2020 at 8:54 PM James A. Bednar ***@***.***> wrote: I guess whether this is a bug or a requested feature depends on your outlook on life. :-)

If it's code you wrote, someone's suggesting a feature enhancement. If it's code someone else wrote, it's a bug report! :)