On Thursday, January 20, 2011 10:35:46 PM UTC-4, 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 = []):
See http://docs.python.org/tutorial/controlflow.html#default-argument-values Read the text following "Important warning: The default value is evaluated only once.". André > 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 !!! -- http://mail.python.org/mailman/listinfo/python-list
