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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def GetDefaultServicePeriod(self):
 """Return the default ServicePeriod. If no default ServicePeriod has been set select the default depending on how many ServicePeriod objects are in the Schedule. If there are 0 make a new ServicePeriod the default, if there is 1 it becomes the default, if there is more than 1 then return None. """

    if not self._default_service_period:
      if len(self.service_periods) == 0:
        self.NewDefaultServicePeriod()
      elif len(self.service_periods) == 1:
        self._default_service_period = self.service_periods.values()[0]
    return self._default_service_period