On Mon, Feb 22, 2010 at 4:10 PM, C M Caine <cmca...@googlemail.com> wrote:
> Or possibly strange list of object behaviour
>
> IDLE 2.6.2
> >>> class Player():
> hand = []
>
>
> >>> Colin = Player()
> >>> Alex = Player()
> >>>
> >>> Players = [Colin, Alex]
> >>>
> >>> def hands():
> for player in Players:
> player.hand.append("A")
>
> >>> hands()
> >>>
> >>> Colin.hand
> ['A', 'A']
> >>> Alex.hand
> ['A', 'A']
>
> I would have expected hand for each object to be simply ['A']. Why
> does this not occur and how would I implement the behaviour I
> expected/want?
>
> Thanks in advance for your help,
> Colin Caine
This comes from the nature of the list object. Python lists are pass/shared
as reference objects. In your case, both Colin and Alex are pointing to the
Player object's copy of hands - they both get a reference to the same
object.
If you want to create different hand lists you could do something like this:
class Player:
def __init__(self, hand=None):
if isinstance(hand, list):
self.hand = hand
else:
print "Player needs a list object for its hand!"
ex:
In [11]: Alan = Player()
Player needs a list object for its hand!
In [12]: Alan = Player([])
In [13]: Jim = Player([])
In [14]: Alan.hand.append(3)
In [15]: Jim.hand
Out[15]: []
HTH,
Wayne
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