human
Solve the following python programming problem given the following code:
def __init__(self, hass, name, children, commands, attributes) : 
    'Initialize the Universal media device.' 
    self.hass = hass 
    self._name = name 
    self._children = children 
    self._cmds = commands 
    self._attrs = attributes 
    self._child_state = None 
    def on_dependency_update(* _) : 
        'Update ha state when dependencies update.' 
        self.update_ha_state (True) 
depend = copy (children) 
    for entity in attributes.values () : 
        depend.append (entity [0]) 
track_state_change (hass, depend, <MASK>) 
    
    Given the code above, what is a proper replacement for <MASK>?
assistant
#Here is a proper replacement for <MASK>.
def on_dependency_update(