Get an old param value after it was changed

Panel
,
1

Hello! How could I get the previous (old) value of the parameter? Now I have such code:

import param

class MainController(param.Parameterized):
    colormap = param.ObjectSelector(default='viridis', objects=['viridis', 'fire'])
   
    @param.depends("colormap")
    def _colormap(self, ):
        print('old value', ?)
        print('new value', self.colormap)
        
m = MainController()
pn.Row(m)
2

Not sure if old values are stored somewhere.

Maybe this works for whatever you are trying to do:

import param
import panel as pn
pn.extension()


class MainController(param.Parameterized):
    colormap = param.ObjectSelector(default='viridis', objects=['viridis', 'fire'])

    @param.depends("colormap", watch=True)
    def _colormap(self, ):
        print('old value', self.old_colormap)
        print('new value', self.colormap)
        #self.old_colormap = self.colormap
        
    # the main function that will do whatever you are trying to do, or some other function.    
    def main_func(self):
        self.old_colormap = self.colormap
        
m = MainController()
pn.Row(m.param, m.main_func)
1 Like
3

Thank you @dhruvbalwada! That works like a charm.

1 Like