Carl Witty wrote:
> On Sat, Mar 28, 2009 at 5:28 AM, Jason Grout
> <jason-s...@creativetrax.com> wrote:
>> Aha, the one custom infix operator that I know of in Sage.
>>
>> In the backslash operator and in the article posted, the rmul only
>> stored the argument and the __mul__ only performed the operation. Are
>> you always guaranteed that __rmul__ will be called right before __mul__
>> for the same invocation of the operation?
>
> Hmm... probably not. Consider
> A *emul* (B *emul* C)
> Since multiplication is left-associative, this is:
> (A*emul)*((B*emul)*C)
>
> This is probably (I don't know if Python guarantees left-to-right
> evaluation, but I'm guessing it does) evaluated in this order:
>
> t1 = A*emul
> t2 = B*emul
> t3 = t2*C
> t4 = t1*t3
>
> So for safe general-purpose use, A*emul needs to return a new object.
>
Okay, how about this:
class inline_operator:
def __init__(self, function, left=None, right=None):
self.function = function
self.left = left
self.right = right
def __rmul__(self, left):
if self.right is None:
return inline_operator(self.function, left=left)
else:
return self.function(left, self.right)
def __mul__(self, right):
if self.left is None:
return inline_operator(self.function, right=right)
else:
return self.function(self.left, right)
# EXAMPLE
a=[1,2,3]
b=[3,4,5]
@inline_operator
def emul(a,b):
return [i*j for i,j in zip(a,b)]
# Returns [3,8,15]
a *emul* b
Jason
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