[SOLVED] Dynamic initialization of Traits Range object

Dynamic initialization of Traits Range object

I'm having trouble trying to dynamically initialize a Traits Range object.

The following code is a very simple example of what I'm trying to do, but sadly fails with the following type error:

TypeError: unsupported operand type(s) for -: 'int' and 'code'

from traits.api import HasTraits, Int, Range
from traitsui.api import View, Item

class DynamicRange(HasTraits):
    """Dynamic initialisation of a Range object"""
    N = Int()
    R = Range(low=0, high='N')

    traits_view = View(Item('R'), Item('N'))

    def __init__(self, N):
        self.N = N         # initial parameter value for N

    def _N_default(self):
        return self.N

Robject = DynamicRange(N=10)
Robject.configure_traits()

The code works if I replace the definition of 'R' with: R = Range(low=0, high=10), but then of course I don't get the dynamic initialization of the Range's high parameter that I'm seeking.

All suggestions gratefully accepted.

* Edit after Jonathan's response *

Here's the simple solution to my question using Jonathan's helpful suggestion below:

from traits.api import HasTraits, Range
from traitsui.api import View, Item

class DynamicRange(HasTraits):
    """Dynamic initialisation of a Range object"""
    traits_view = View(Item('R'))

    def __init__(self, N):
        self.add_trait("R", Range(0, N))

Robject = DynamicRange(N=30)
Robject.configure_traits()

Solution

One method would be to define the trait not in the usual way, but within __init__, thus:

    self.add_trait("R", Range(0, N))

See http://docs.enthought.com/traits/traits_user_manual/advanced.html#per-object-trait-attributes