def add(self, name, installer, args, api=2):
    'Convenience method for .append(Callback())'
    callback = Callback(name, installer, args, api)
    self.append(callback)
Convenience method for .append(Callback())
def add(self, name, installer, args, api=2):
    
    callback = Callback(name, installer, args, api)
    self.append(callback)