# works
class TFloatObject(TObject):
  ...
  def add(self, other):
    assert(isinstance(other, TObject))

    if isinstance(other, TIntObject):
      return TFloatObject(self.val + other.val)
    elif isinstance(other, TFloatObject):
      return TFloatObject(self.val + other.val)
    else:
      raise Exception("Incompatibe types")


# fails
class TFloatObject(TObject):
  ...
  def add(self, other):
    assert(isinstance(other, TObject))

    if isinstance(other, TIntObject) or  isinstance(other, TFloatObject):
      return TFloatObject(self.val + other.val)
    else:
      raise Exception("Incompatibe types")