Question

I have several variables like:

class X(object):
    ...

class XY(X):
    ...

class XZ(X):
    ...

class XA(X):
    ...

y=XY()
z=[XZ(i) for i in range(1,10)]
a=[XA(i) for i in range(1,10)]

I would like to have a listlike view(including iteration and length) of the different variable y and the variables inside z and a.

this is for the sake of convenience w/out any worries about performance.
I could just do

view = [self.y] + self.z + self.a

each time but that seems to be breaking the DRY principle.

Edit: to clarify that this isn’t about taking the instance variables of a class. I just want a view class, probably implementing a list like interface that forwards to other variables.
Or would it be better to make a closure that returns a view list when you call it(since I don’t care about performance). Which is simpler/more pythonic/a better idea? How would I implement a list like forwarding class?., ect.

Answer 1

If I understand correctly you want to “chain” the iterators of self.z and self.a and add self.y to that. Perhaps this does what you want:

import itertools
itertools.chain(self.a, self.z, [self.y])

The cleanest would probably be to implement it like this:

class C(object):
    def __init__(self, y, z, a):
        # ...

    def __iter__(self):
        return itertools.chain(self.a, self.z, [self.y])