Why is this wrong? The way to sort [3, 1, 2] is to put 1 first (index 1), then 2 (index 2), then 3 (index 0), so the correct answer is [1, 2, 0]. What answer did you expect and why? Maybe you are confusing np.argsort with np.sort?

argsort's behavior is subtle, and many people expect it to do something different than what it is documented to do (see #8757 and other closed issues). But it is behaving as designed and documented.

I am so sorry to misunderstand the code and the documents. Sorry for that.