'Add the value at the specified position, padding out missing entries.
@type itemAndValue: C{tuple}
@param item: A tuple of (item, value).  The I{item} is the 0-based
index in the list at which the value should be placed.  The value is
is an L{object} to put in the list.'

def setitem(self, itemAndValue):

    (item, value) = itemAndValue
    diff = ((item - len(self.L)) + 1)
    if (diff > 0):
        self.L.extend(([None] * diff))
    self.L[item] = value
