add_callback¶

echo.add_callback(instance, prop, callback, echo_old=False, priority=0, validator=False)[source]¶

Attach a callback function to a property in an instance

Parameters:

instance: The instance to add the callback to
propstr: Name of callback property in instance
callbackfunc: The callback function to add
echo_oldbool, 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)
priorityint, optional: This can optionally be used to force a certain order of execution of callbacks (larger values indicate a higher priority).
validatorbool, optional: Whether the callback is a validator, which is a special kind of callback that gets called before the property is set. The validator can return a modified value (for example it can be used to change the types of values or change properties in-place) or it can also raise an exception.

Examples

class Foo:
    bar = CallbackProperty(0)

def callback(value):
    pass

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

echo