getting unexpected value error from the np.dot

Question

in one of my functions, I called the diff()

diffs = Tranche.diff(tranche_face, rate, new_rates)

# class level method of diff inside Tranche class
    @classmethod
    def diff(cls, tranche_face, last_rates, new_rates):
        step1 = [x - y for x, y in zip(last_rates, new_rates)]
        step2 = [abs(x / y) for x, y in zip(step1, last_rates)]
        return np.dot(tranche_face, step2) / sum(tranche_face)  # np.dot is from numpy

Below is the parameter getting passed-in:

tranche_face = [22683499.454199996, 5670874.863549999]
rate = [0.05, 0.08]
new_rates = [0.07061657282343299, 0.06874103335919428]

And I am getting the below error for diff:

ValueError: shapes (2,) and (4,) not aligned: 2 (dim 0) != 4 (dim 0)

Below is the functionality I would like to achieve with diff:

to clarify, the first element in each list corresponds to everything with A in the formula, and the second represents B (last rate is just the rate, face is the notional)

Answer 1

Problem solved, I forgot to reset the new_rates to be empty. Just a logic in my simulation function.