echo.add_callback(instance, prop, callback, echo_old=False, priority=0)

Attach a callback function to a property in an instance



The instance to add the callback to

prop : str

Name of callback property in instance

callback : func

The callback function to add

echo_old : bool, optional

If True, the callback function will be invoked with both the old and new values of the property, as func(old, new). If False (the default), will be invoked as func(new)

priority : int, optional

This can optionally be used to force a certain order of execution of callbacks (larger values indicate a higher priority).


class Foo:
    bar = CallbackProperty(0)

def callback(value):

f = Foo()
add_callback(f, 'bar', callback)