<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def observe(self, ob):
 """ Add the Observe option. :param ob: observe count """

        option = Option()
        option.number = defines.OptionRegistry.OBSERVE.number
        option.value = ob
        self.del_option_by_number(defines.OptionRegistry.OBSERVE.number)
        self.add_option(option)