Am 03.12.2010 23:11, schrieb Arnaud Delobelle:
OAN<programm...@toomuchcookies.net> writes:
Hi,
i was having a problem with class attributes initiated outside of
__init__. This code is a demonstration of what i mean:
class A():
mylist = []
def __init__(self):
self.mylist.append(1)
pass
class B(A):
def __init__(self):
A.__init__(self)
self.mylist.append(2)
v = A()
print 'v:',v.mylist
x = B()
print 'x:',x.mylist
y = B()
print 'y:',y.mylist
z = A()
print 'z:',z.mylist
print 'v:',v.mylist
I would expect the following result:
v: [1]
x: [1, 2]
y: [1, 2]
z: [1]
v: [1]
Who wouldn't, right? But actually python 2.6(.6) gives me the
following result:
v: [1]
x: [1, 1, 2]
y: [1, 1, 2, 1, 2]
z: [1, 1, 2, 1, 2, 1]
v: [1, 1, 2, 1, 2, 1]
The four variables v,x,y and z now actually share the same 'mylist'!!
To get the correct results, i have to initialize 'mylist' inside of
the __init__ method!
Yes. See below.
I think this behaviour is totally wrong, since it seems
A.__init__(self) is changing the value inside of A() not inside of the
object variable 'self' (that should be x or y)!!
It's not wrong at all. You expect "mylist" to behave as an instance
attribute, but you defined it as a class attribute. Instance attributes
are naturally initialised in the __init__() method.
Could you please point me to a reference in the doc??
Thanks in advance.
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