code: def field_get_subfields(field):
      
      pairs = {}
      for key, value in field[0]:
          if key in pairs and pairs[key] != value:
              pairs[key].append(value)
          else:
              pairs[key] = [value]
      return pairs
docs: Given a field, will place all subfields into a dictionary
      Parameters:
       * field - tuple: The field to get subfields for
      Returns: a dictionary, codes as keys and a list of values as the value