text: class VolumeConstraint(object):
      def __init__(self, time, location):
          self.time = time
          self.location = location
  
      def __eq__(self, other):
          return self.time == other.time and self.location == other.location
  
      def __hash__(self):
          return hash(str(self.time)+str(self.location))
  
      def __str__(self):
          return '(' + str(self.time) + ', '+ str(self.location) + ')'
  