import numpy
terms = numpy.array([1, -4, 5, -7, 4, 3, -5, 6, 13, -21])
sums = []
for i in range(len(terms)):
    terms_i = terms[:i+1]

    sums_i = terms_i[::-1].cumsum()[::-1]

    start_term_i = sums_i.argmax()
    sums_i_max = sums_i[start_term_i]
    sums.append((start_term_i, sums_i_max))

sums = numpy.array (sums)

end_term = sums [:,1].argmax()
start_term,sums_max = sums[end_term]

print("Max sum: " + str(sums_max))
print()