inside.py

class Part(object):
    inside = False

class Object(list):
    def __init__(self):
        self[0] = Part()
        self[1] = Part()

def object_inside(o):
    return all(part.inside == True for part in o)

def test_inside():
    o = Object()
    for part in o:
        part.inside = True
    assert True == object_inside(o)