On Dec 21, 7:34 am, Marc 'BlackJack' Rintsch <bj_...@gmx.net> wrote: > On Sun, 21 Dec 2008 12:45:32 +0000, Duncan Booth wrote: > > You seem to have made an unwarranted assumption, namely that a binary > > operator has to compile to a function with two operands. There is no > > particular reason why this has to always be the case: for example, I > > believe that C# when given several strings to add together optimises > > this into a single call to a concatenation method. > > > Python *could* do something similar if the appropriate opcodes/methods > > supported more than two arguments: > > > a+b+c+d might execute a.__add__(b,c,d) allowing more efficient string > > concatenations or matrix operations, and a%b%c%d might execute as > > a.__mod__(b,c,d). > > But that needs special casing strings and ``%`` in the comiler, because > it might not be always safe to do this on arbitrary objects. Only in > cases where the type of `a` is known at compile time and ``a % b`` > returns an object of ``type(a)``.
'x+y' makes no guarantees whatsoever. It could return an object of type(x), type(y), or neither. 'a%b' in the case of strings is just, str.__mod__, returning string. In a+b+c, 'a' gets dibs over what the rest see, so there's no more danger in the multi-ary case, than in binary; and that hasn't stopped us before. You might be confusing the cases of arbitrary operators vs. uniform operators. 'a' does not get dibs in 'a+b*c'; 'b*c' are allowed to carry out their affairs. But in 'a+b+c', 'a*b*c', 'a%b%c', and so on, 'a' has final say on b's and c's behaviors via its return value, so loses nothing by combining such a call. In short, you can force it anyway, so it's syntactic sugar after that. -- http://mail.python.org/mailman/listinfo/python-list
