New instance of a class : not reset?

[MRAB]

On 21/01/2011 02:35, Jean-Francois wrote:
> Hi,
>
> In the following example, I don't understand why attribute 'data' is
> not reset when I get the new instance of Bag
> It works if I make a copy (data[:]) but I want to understand why
>
> Thanks
>
>
> class Bag(object):
> 	def __init__(self, data = []):
> 		self.data = data
> 		#self.data = data[:]
> 	def add(self, x):
> 		self.data.append(x)
>
> bag = Bag()
> print bag.data
> bag.add('toto')
> print bag.data
> bag = Bag()      # new instance of Bag, all attributes clear?
> print bag.data   # 'toto' is still there !!!

See:
     http://effbot.org/zone/default-values.htm