• "Hubspot"-"How deep" mission. (3) is tuple or int?

Question related to mission How Deep

 

I can't understand, why right answer from 9th test "how_deep((1,(2),(2,(3))))" equals 3, not 2. If we test "type((3))", it returns 'int', not 'tuple'. Also I can't understand why my function returns 3 in 'Check', but 2 in 'Run'. Please, could you give me a clue?