The left associativity should be the less disturbing choice. Using parenthesis to force right associativity will be not too painful. How many matrices in long product are involved concretely in Numpy projects ? On the other hand, Nathaniel proposed a new way to evaluate associative operators, and I really think that would be the best way to manage products of matrices. The idea is fir example to see A@B@C@D as __atmul__(A, B, C, D). Christophe BAL