Hi,
I am defining a parent and elements in the category of modules over QQ. The
proper way would be to use the category framework:
from sage.structure.parent import Parent
from sage.structure.element import ModuleElement
from sage.categories.modules import Modules
class MElement(ModuleElement):
def __init__(self, parent, x):
ModuleElement.__init__(self, parent)
self._x = x
def _repr_(self):
return 'element {}'.format(self._x)
def _rmul_(self, e): # defines scalar multiplication
R = self.parent()
return R.element_class(R, e * self._x)
class M(Parent):
Element = MElement
def __init__(self):
Parent.__init__(self, base=QQ, category=Modules(QQ))
Then the following works fine:
sage: P = M()
sage: five = P.element_class(P, 5); five
element 5
sage: 2 * five
element 10
My question is: why should I use `ModuleElement` instead of just `Element`?
If I use `Element`, the scalar multiplication is not detected by the
coercion system. So I am forced to use `ModuleElement`.
Since my parent is in the category of modules over QQ, then I think
elements of the parent should be automatically treated as module elements,
and using `Element` should just be ok.
What do you think?
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