code: def _m2m_rev_field_name(model1, model2):
      
      m2m_field_names = [
          rel.get_accessor_name() for rel in model1._meta.get_fields()
          if rel.many_to_many
             and rel.auto_created
             and rel.related_model == model2
      ]
      return m2m_field_names[0]
docs: Gets the name of the reverse m2m accessor from `model1` to `model2`
  
      For example, if User has a ManyToManyField connected to Group,
      `_m2m_rev_field_name(Group, User)` retrieves the name of the field on
      Group that lists a group's Users. (By default, this field is called
      `user_set`, but the name can be overridden).