src/functions/mase.py

import numpy


def MASE(Actual, Predicted):
    '''
    Mean Absolute Scaled Error (MASE) 
    '''
    values = []
    for i in range(1, len(Actual)):
        values.append(abs(Actual[i] - Predicted[i]) /
                      (abs(Actual[i] - Actual[i - 1]) / (len(Actual) - 1)))

    return numpy.mean(values)