Question

My python program returns a list containing data of sub-list. Each sub-list contains the unique id of an article and the parent id of that article viz

pages_id_list ={ {22, 4},{45,1},{1,1}, {4,4},{566,45},{7,7},{783,566}, {66,1},{300,8},{8,4},{101,7},{80,22}, {17,17},{911,66} }

In each sub-list, the data is structured this way {*article_id*, *parent_id*}
If the article_id and parent_id are the same it obviously mean that article has no parent.

I would like to sort the data using minimal code such that for each article, I can readily
access a list of it’s children and grandchildren (nested data) if available. For example (using the example data above) I should be able to print at the end of the day:

 1
 -45
 --566
 ---783
 -66
 --911

…. for article id 1

I could only sort out the highest level (Ist and 2nd generation) ids. Having problem getting the 3rd and subsequent generations.

This is the code I used:

highest_level = set()
first_level = set()
sub_level = set()

for i in pages_id_list:
    id,pid = i['id'],i['pid']

    if id == pid:
        #Pages of the highest hierarchy
        highest_level.add(id)

for i in pages_id_list:
    id,pid = i['id'],i['pid']

    if id != pid :
        if pid in highest_level:
            #First child pages
            first_level.add(id)
        else:
            sub_level.add(id)

My code sadly does not work.

Any help/nudge in the right direction will be appreciated.
Thanks

David

Answer 1

Maybe something like this:

#! /usr/bin/python3.2

pages_id_list = [ (22, 4),(45,1),(1,1), (4,4),(566,45),(7,7),(783,566), (66,1),(300,8),(8,4),(101,7),(80,22), (17,17),(911,66) ]

class Node:
    def __init__ (self, article):
        self.article = article
        self.children = []
        self.parent = None

    def print (self, level = 0):
        print ('{}{}'.format ('\t' * level, self.article) )
        for child in self.children: child.print (level + 1)

class Tree:
    def __init__ (self): self.nodes = {}

    def push (self, item):
        article, parent = item
        if parent not in self.nodes: self.nodes [parent] = Node (parent)
        if article not in self.nodes: self.nodes [article] = Node (article)
        if parent == article: return
        self.nodes [article].parent = self.nodes [parent]
        self.nodes [parent].children.append (self.nodes [article] )

    @property
    def roots (self): return (x for x in self.nodes.values () if not x.parent)

t = Tree ()
for i in pages_id_list: t.push (i)
for node in t.roots: node.print ()

This creates a tree structure which you can traverse in order to get all subitems. You can access any article via t.nodes [article] and get its children via t.nodes [article].children.

The output of the print method is:

1
    45
        566
            783
    66
        911
4
    22
        80
    8
        300
7
    101
17