I do not really know about it, but it seems to me, by experience, that jpcgt is actually right. Following example: If I use following code
t = [] # implicit instantiation
t = t.append(1)
in the interpreter, then calling t gives me just "t" without any list, and if I append something else, e.g.
t = t.append(2)
I get the error "'NoneType' object has no attribute 'append'". If, however, I create the list by
t = list() # explicit instantiation
then it works fine.