docs: def to_ped(self):
          """
          Return a generator with the info in ped format.
          
          Yields:
              An iterator with the family info in ped format
          """
          
          ped_header = [
              '#FamilyID',
              'IndividualID',
              'PaternalID',
              'MaternalID', 
              'Sex',
              'Phenotype',
          ]
          
          extra_headers = [
              'InheritanceModel',
              'Proband',
              'Consultand',
              'Alive'
          ]
          
          for individual_id in self.individuals:
              individual = self.individuals[individual_id]
              for info in individual.extra_info:
                  if info in extra_headers:
                      if info not in ped_header:
                          ped_header.append(info)
          
          self.logger.debug("Ped headers found: {0}".format(
              ', '.join(ped_header)
          ))
          
          
          
          yield '\t'.join(ped_header)
          
          for family_id in self.families:
              for individual_id in self.families[family_id].individuals:
                  individual = self.families[family_id].individuals[individual_id].to_json()
                  ped_info = []
                  ped_info.append(individual['family_id'])
                  ped_info.append(individual['id'])
                  ped_info.append(individual['father'])
                  ped_info.append(individual['mother'])
                  ped_info.append(individual['sex'])
                  ped_info.append(individual['phenotype'])
              
                  if len(ped_header) > 6:
                      for header in ped_header[6:]:
                          ped_info.append(individual['extra_info'].get(header, '.'))
              
                  yield '\t'.join(ped_info)