This existing code works fine…

item_list = order_items()

def order_items():
l = []
for id in items:
l.append(items[id])
l.sort()
return l

We print out XML and have a value for sku

    lines.append("tt<sku>%s</sku>" % p.sku)

How would the sort be modified to sort based on the value of sku?