Dear all,
i just found that there is a difference how the __rmul__ method works
for usual classes and for cdefined classes. A short example (yes,
usually i don't want that __mul__ changes self...):
cdef class MulC:
cdef object r
def __init__(self,r):
self.r = r
def __repr__(self):
return str(self.r)
def __mul__(MulC self,s):
self.r=self.r*s
return self
def __rmul__(MulC self,s):
self.r=self.r*s
return self
class MulP:
def __init__(self,r):
self.r = r
def __repr__(self):
return str(self.r)
def __mul__(self,s):
self.r=self.r*s
return self
def __rmul__(self,s):
self.r=self.r*s
return self
and now:
sage: M=MulP(3)
sage: M*3
9
sage: 3*M
27
This is the behaviour that i want.
But for the cdefined class i get a traceback:
sage: M=MulC(3)
sage: M*3
9
sage: 3*M
---------------------------------------------------------------------------
TypeError Traceback (most recent call
last)
...
TypeError: unsupported operand parent(s) for '*': 'Integer Ring'
and ...
The Traceback mentions something about coercion. So, is it true that
3*M tries coercion, if M is a cdefined class, but tries to apply
M.__rmul__(3) if M is a python class? Why? Is there a way to work
around coercion in this case?
Yours
Simon
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