Ksenia Marasanova wrote:
> I want to sort this list with the following rules:
> 1. The parent must always come before the children in the list
> 2. Nodes with the same parent must be sorted by 'ord_number'
>
> The first rule is easy, cause I can use 'url' for it. List with nodes
> is coming from the database, so I just do "ORDER BY url".
I think you cannot get away with your first rule, but have to operate on the
full path instead. Otherwise the position of inner nodes would sometimes be
determined by their url and sometimes by their ord_number *during* *the*
*same* *sort*.
class Node(object):
nodes = {} # defeats garbage collection
def __init__(self, id, name, ord_number, parent_id, url):
self.id = id
self.name = name
self.ord_number = ord_number
self.parent_id = parent_id
self.url = url
assert id not in self.nodes
self.nodes[id] = self
def get_path(self):
node = self
path = []
while node is not None:
path.append(node)
node = self.nodes.get(node.parent_id)
path.reverse()
return path
def get_key(self):
return [node.ord_number for node in self.get_path()]
def __cmp__(self, other):
return cmp(self.get_key(), other.get_key())
def __str__(self):
return "%s %s" % (self.name, self.get_key())
nodes = [Node(**row) for row in data]
# key argument not necessary, but should be faster
nodes.sort(key=Node.get_key)
I'm too lazy to do the test cases, so you have to check it yourself.
Peter
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