Hi, Prasoon has described here precisely the problems with extending sympy with user defined types:
https://groups.google.com/d/topic/sympy/QV6m9Nfp9kw/discussion Currently the only way to robustly do that is through _op_priority as Julien described. The usual Python approach (NotImplemented) doesn't work, because if for example Mul.__add__ thinks it knows how to work with user's type, it will not return NotImplemented and thus the user has no way of overriding it. The other way to implement this is called "multiple dispatch" (http://en.wikipedia.org/wiki/Multiple_dispatch). I mention it at the end of my blog post [1]. Julia has multiple dispatch implemented, see here how it works there: http://docs.julialang.org/en/latest/manual/methods/ This is also related to Matthew's idea to use "mul" instead of "Mul": http://code.google.com/p/sympy/issues/detail?id=3909 since the new function "mul" would (or could) use multiple dispatch to decide what exactly it will do based on parameters, and I think that it would just be a quick O(1) dictionary lookup based on argument types. Then Symbol.__mul__, Integer.__mul__, Add.__mul__, Mul.__mul__, ..., would just call the function "mul". So it should be fast. The user would then register his own new types into SymPy and register his own function for "mul", which would get called whenever he wants. This would among other things allow to provide faster implementation of SymPy core, as the faster core (implemented in Cython or C++ for example) would simply register its own faster types and faster implementation of "mul". We can also do multiple dispatch for things like "series" etc., though for functions of just one argument the default Python method resolution should work well (i.e. the faster core simply implements its own "series" method). I think the problem is for functions like "mul", which accept two arguments. I suggest to read the Julia docs and learn from there all the details how exactly they decide which method gets called. I think they have thought about this thoroughly and so we should learn from their experience. Ondrej [1] http://ondrejcertik.blogspot.com/2013/07/my-impressions-from-scipy-2013.html -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sympy+unsubscr...@googlegroups.com. To post to this group, send email to sympy@googlegroups.com. Visit this group at http://groups.google.com/group/sympy. For more options, visit https://groups.google.com/groups/opt_out.
