Here is a workaround that I dislike (but it works):
class BeamParameter(Expr):
__slots__ = ['z', 'z_r']
def __new__(cls, z, z_r):
inst = Expr.__new__(cls, z, z_r)
inst.z = z
inst.z_r = z_r
return inst
@property
def q(self):
return self.z+I*self.z_r
Now I can do:
>>>bp = BeamParameter(1,2)
>>>bp.q
1+I*2
But I would like to have:
>>>bp
1+I*2
On 10 June 2011 23:06, [email protected] <
[email protected]> wrote:
> BeamParameter should be just a complex number. As there is no Complex class
> in sympy I have tried to base it on Add.
>
> I need some additional fields and methods to implement the formalism, but
> if BeamParameter returns complex number created from the two arguments in
> the constructor the rest is easy.
>
> The nested example you gave should return x+I*y+I*z. This is complete
> nonsense from physical point of view, but the user is free to do it.
>
> I have tried to do it without __slots__ and __new__ and use __init__
> instead but then isinstance(q, BeamParameter) returns False. I have no idea
> why it's not True?
>
>
> On 10 June 2011 22:34, Aaron Meurer <[email protected]> wrote:
>
>> I'm not the best person to answer this, but probably you are doing
>> this the wrong way.
>
> I'm pretty sure you are right about me being wrong :)
>
>
>> I suppose to know how you should do it, I would
>> need to know more about how you expect this class to work. What do
>> you expect BeamParamter(0, 1) to return? How about
>> BeamParameter(BeamParameter(x, y), z) (nested classes)?
>>
>> Aaron Meurer
>>
>> On Fri, Jun 10, 2011 at 12:10 PM, [email protected]
>> <[email protected]> wrote:
>> > Hi,
>> >
>> > I am trying to create a class that is basically the sum of two arguments
>> > given in the constructor. Here is what I have done (simplified example
>> with
>> > omitted arguments and slots):
>> >
>> > class BeamParameter(Add):
>> >
>> > __slots__ = ['x', 'y']
>> >
>> > def __new__(cls, x, y):
>> > obj = Add.__new__(cls, x, I*y)
>> > obj.x = x
>> > obj.y = y
>> > return obj
>> >
>> >
>> > It works ok when Add returns Add:
>> >>>>q=BeamParameter(1,1)
>> >>>>q
>> > 1+I*1
>> >
>> > But it fails when Add returns Mul:
>> >>>>q=BeamParameter(0,1)
>> > ---> 54 obj.x = x
>> > AttributeError: 'Mul' object has no attribute 'x'
>> >
>> >
>> > The __slots__ are lost somewhere for some reason. I'm afraid that I
>> don't
>> > understand why. Maybe I should not use Add as a superclass. Do you have
>> any
>> > solutions?
>> >
>> > Stefan
>> >
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