I use data from https://en.wikipedia.org/wiki/Wilcoxon_signed-rank_test, W value is 9. But, for the following code W value is 18, what is the reason?

# Wilcoxon signed-rank test
from numpy.random import seed
from numpy.random import randn
from scipy.stats import wilcoxon
# seed the random number generator
# generate two independent samples


# compare samples
stat, p = wilcoxon(a,b)
print('Statistics=%.3f, p=%.3f' % (stat, p))
# interpret
alpha = 0.05
if p > alpha:
    print('Same distribution (fail to reject H0)')
    print('Different distribution (reject H0)')

If you look at the wikipedia page of Wilcoxon signed-rank test, under the section of the original test, it's mentioned that

The original Wilcoxon's proposal used a different statistic. Denoted by Siegel as the $T$ statistic, it is the smaller of the two sums of ranks of given sign; in the example given below, therefore, $T$ would equal $3+4+5+6=18$

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