PyCSP Revisited

PyCSP was introduced two years ago and has since been used by a number of programmers, especially students. The original motivation behind PyCSP was a conviction that both Python and CSP are tools that are especially well suited for programmers and scientists in other fields than computer science. Working under this premise the original PyCSP was very similar to JCSP and the motivation was simply to provide CSP to the Python community in the JCSP tradition. After two years we have concluded that PyCSP is indeed a usable tool for the target users; however many of them have raised some of the same issues with PyCSP as with JCSP. The many channel types, lack of output guards and external choice wrapped in the select-then-execute mechanism were frequent complaints. In this work we revisit PyCSP and address the issues that have been raised. The result is a much simpler PyCSP with only one channel type, support for output guards, and external choice that is closer to that of occam than JCSP.