def test4(self):
s = Solution()
expr = ['+', 1, 2, ['*', 2, 3], ['-', 4, 5], ['/', 8, 2]]
res = s.eval(expr)
self.assertEqual(res, 12)
def test1(self):
s = Solution()
expr = ['+', 1, 2, ['*', 1, 3]]
res = s.eval(expr)
self.assertEqual(res, 6)
def test3(self):
s = Solution()
expr = ['+', ['*'], ['-'], ['/']]
res = s.eval(expr)
self.assertEqual(res, 1)
