Organising information: trees

Communication 1

Today there will be also the official assessment of the course run by the University

Communication 2

I will integrate the official assessment questionnaire with another brief one that will be presented to you after the final written examination

Any question about the previous lecture?

Historic hero: Gabriel Garcia Marquez

He was a novelist, and won the Nobel Prize for Literature in 1982

He is mainly known for his novels: One Hundred Years of Solitude, Love in the Time of Cholera

In the One Hundred Years of Solitude he narrates the story of seven different generations of people of the Buendia family

At the beginning of the book there is the Buendia family tree, for helping the reader to follow the story

Other uses of trees

Recursive algorithm: we have used a tree for showing the execution of the recursive calls to the Fibonacci algorithm implemented by means of the divide and conquer approach

Document markup: languages such as TEI and HTML are examplars of languages which allows one to construct hierarchies of markup elements for structurally and semantically annotating a text

Tree and Python

There is no built-in implementation of the tree data structure in Python

We use the external anytree package

Constructor for nodes:
def Node(name, parent=None)

Each node must specify a name (as a string) and a parent – if the parent is not specified then it will assume None as value and it is implicitly defined as the root node of a tree

Example

from anytree import Node

root = Node("html")

head = Node("head", root)
title = Node("title", head)

body = Node("body", root)
paragraph_1 = Node("p", body)
paragraph_2 = Node("p", body)

The siblings of a certain parent are actually ordered among them – the order is defined by the order of insertion as a child of that particular parent

For instance, in the example, paragraph_1 precedes paragraph_2

Hooks

• <node>.children returns a tuple listing all the children of a node

• <node>.parent returns the parent of a node

• <node>.descendants returns a tuple listing all the descendants of a node (including its children)

• <node>.ancestors returns a tuple listing all the ancestors of a node (including its parent)

• <node>.siblings returns a tuple listing all the siblings of a node

• <node>.root returns the root node of the tree where a node is contained