At Thursday 4/1/2007 17:26, Emin wrote:
I got some unexpected behavior in getattr and copy.deepcopy (see
transcript below). I'm not sure if this is actually a bug in
copy.deepcopy or if I'm doing something too magical with getattr.
Comments would be appreciated.
Both examples are different. #1 stores a *bound* method into an
instance attribute. Bound methods carry a reference to "self", this
creates a cyclic reference that may cause problems to the garbage
collector (and confuses deepcopy, apparently).
#2 uses and *unbound* method and it's the usual way.
>>> class a:
... def foo(self):
... print 'hi'
...
>>> class b(a): #1
... def __init__(self):
... self.y = getattr(self,'foo')
>>> class b(a): #2
... def __init__(self):
... self.x = self.__class__.__bases__[0].__dict__['foo']
For #2 you can simply say:
class b(a):
x = a.foo
If you have to choose at runtime (a simplified version of your own code):
class b(a):
def __init__(self):
name = select_method_to_use(..., default="foo")
self.x = getattr(a, name)
You *know* your bases because you wrote them in the class statement
(or use super() instead of playing with __bases__); and getattr works
fine here so you don't need to mess with the __dict__ details.
(Note that #1 was *almost* right, you had to replace self by the base class)
--
Gabriel Genellina
Softlab SRL
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