From your mailing list link:
because the one-sided tests can be backed out from the two-sided
tests. (With symmetric distributions one-sided p-value is just half
of the two-sided pvalue)
It goes on to say that scipy always gives the test statistic as signed. This means that given p and t values from a two-tailed test, you would reject the null hypothesis of a greater-than test when p/2 < alpha and t > 0, and of a less-than test when p/2 < alpha and t < 0.