old_contents: class Lattice(object):
  
      def __init__(self, name):
          self.name = name
          self._elements = []
  
      def __getitem__(self, i):
          return self._elements[i]
  
      def __len__(self):
          ''' Get the number of elements in the lattice '''
          return len(self._elements)
  
      def __str__(self):
          print(self._elements)
  
      def get_length(self):
          ''' Get the length of the lattice in meters '''
          total_length = 0
          for e in self._elements:
              total_length += e.get_length()
          return total_length
  
      def add_element(self, element):
          '''
          Add an element to the lattice
          # TODO: modify method to accept a set() arg
          '''
          self._elements.append(element)
  
      def get_elements(self, family='*'):
          '''
          Get all elements of a lattice from a specified family.
          If no family is specified, return all elements
          '''
          if family == '*':
              return self._elements
  
          matched_elements = list()
          for element in self._elements:
              if family in element.families:
                  matched_elements.append(element)
          return matched_elements
  
new_contents: class Lattice(object):
  
      def __init__(self, name):
          self.name = name
          self._elements = []
  
      def __getitem__(self, i):
          return self._elements[i]
  
      def __len__(self):
          ''' Get the number of elements in the lattice '''
          return len(self._elements)
  
      def __str__(self):
          print(self._elements)
  
      def get_length(self):
          ''' Get the length of the lattice in meters '''
          total_length = 0
          for e in self._elements:
              total_length += e.get_length()
          return total_length
  
      def add_element(self, element):
          '''
          Add an element to the lattice
          # TODO: modify method to accept a set() arg
          '''
          self._elements.append(element)
  
      def get_elements(self, family='*'):
          '''
          Get all elements of a lattice from a specified family.
          If no family is specified, return all elements
          '''
          if family == '*':
              return self._elements
  
          matched_elements = list()
          for element in self._elements:
              if family in element.families:
                  matched_elements.append(element)
          return matched_elements
  
      def get_all_families(self):
          families = set()
          for element in self._elements:
              for family in element.families:
                  families.add(family)
  
          return families
  
subject: Add method to get all families of currently loaded elements