text: from Section01_SOLID.DependencyInversionPrinciple.Relationship import Relationship
  from Section01_SOLID.DependencyInversionPrinciple.RelationshipBrowser import RelationshipBrowser
  
  
  class Relationships(RelationshipBrowser):  # low-level
      relations = []
  
      def add_parent_and_child(self, parent, child):
          self.relations.append((parent, Relationship.PARENT, child))
          self.relations.append((child, Relationship.PARENT, parent))
  
      def find_all_children_of(self, name):
          for r in self.relations:
              if r[0].name == name and r[1] == Relationship.PARENT:
                  yield r[2].name
  