[PEP draft 2] Adding new math operators

[Tim Hochberg]

 <gregory.lielens at fft.be> writes
 ...
 >Don't you fear the "backtracking" aspect, i.e. to have to track back the
 >code to check the types of A and B, before knowing the operation which
 >is perfromed by A 'op' B? 
 >I know this is already the case now, for example if A and B are strings,
 >A+B is a concatenation instead of an addition...Fair for me in this case
 >because I consider string and int to be quite different beasts (sorry
 >all perl-lovers :-)), and expect to be able to differentiate them by
 >context quite easily...
 >However, when making the 'op' behavior differ for two very close classes
 >(as array and matrix would obviously be), I think it could be a lot more
 >error-prone...Similar (worst?) to the classical "1/2 == 0 (oops - why
 >not 0.5?)" which pop up sometimes in this newsgroup...


I believe this is why Konrad was suggesting that mixed operations
would raise an error; this would more or less eliminate silent
problems due to "backtracking". If you got at least one of the operand
types correct, the result would either be correct or raise an
error. So in a MatPy environment:

a + b # OK
a.E + b # ValueError
a + b.E # ValueError
a.E + b.E # OK

-tim