1 import sys
2
3 class dummy(object):
4 def __init__(self, val):
5 self.val = val
6
7 class myobj(object):
8 def __init__(self, resources):
9 self._resources = resources
10
11 class ext(myobj):
12 def __init__(self, resources=[]):
13 #myobj.__init__(self, resources)
14 self._resources = resources
15
16 one = ext()
17 one._resources.append(1)
18 two = ext()
19
20 print one._resources
21 print two._resources
22
23 sys.exit(0)
This will print the reference to the object assigned to one._resources for both one and two objects. I would think that two would be an empty array as it is clearly setting it as such if it's not defined when creating the object. Uncommenting myobj.__init__(self, resources) does the same thing. Using super(ext, self).__init__(resources) also does the same thing.
The only way I can get it to work is if I use the following:
two = ext(dummy(2))
I shouldn't have to manually set the default value when creating the object to make this work. Or maybe I do. Any thoughts?
I tried this using Python 2.5 and 2.6.
You should change
def __init__(self, resources=[]):
self._resources = resources
to
def __init__(self, resources=None):
if resources is None:
resources = []
self._resources = resources
and all will be better. This is a detail in the way default arguments are handled if they're mutable. There's some more information in the discussion section of this page.