code: def past_active(self):
          
          forms = []
          stem = self.sfg3et[:-1]
          forms.append(stem+"a")
          forms.append(self.sfg3et+"r")
          forms.append(self.sfg3et)
          forms.append(apply_u_umlaut(stem)+"um")
          forms.append(apply_u_umlaut(stem)+"uð")
          forms.append(apply_u_umlaut(stem)+"u")
          return forms
docs: Weak verbs
          I
          >>> verb = WeakOldNorseVerb()
          >>> verb.set_canonic_forms(["kalla", "kallaði", "kallaðinn"])
          >>> verb.past_active()
          ['kallaða', 'kallaðir', 'kallaði', 'kölluðum', 'kölluðuð', 'kölluðu']
  
          II
          >>> verb = WeakOldNorseVerb()
          >>> verb.set_canonic_forms(["mæla", "mælti", "mæltr"])
          >>> verb.past_active()
          ['mælta', 'mæltir', 'mælti', 'mæltum', 'mæltuð', 'mæltu']
  
          III
          >>> verb = WeakOldNorseVerb()
          >>> verb.set_canonic_forms(["telja", "taldi", "talinn"])
          >>> verb.past_active()
          ['talda', 'taldir', 'taldi', 'töldum', 'tölduð', 'töldu']
  
          IV
          >>> verb = WeakOldNorseVerb()
          >>> verb.set_canonic_forms(["vaka", "vakti", "vakat"])
          >>> verb.past_active()
          ['vakta', 'vaktir', 'vakti', 'vöktum', 'vöktuð', 'vöktu']
  
          :return: