Printing a Tree data structure in Python

Question

I was looking for a possible implementation of tree printing, which prints the tree in a user-friendly way, and not as an instance of object.

I came across this solution on the net:

source: http://cbio.ufs.ac.za/live_docs/nbn_tut/trees.html

class node(object):     def __init__(self, value, children = []):         self.value = value         self.children = children      def __repr__(self, level=0):         ret = "\t"*level+repr(self.value)+"\n"         for child in self.children:             ret += child.__repr__(level+1)         return ret 

This code prints the tree in the following way:

'grandmother'     'daughter'         'granddaughter'         'grandson'     'son'         'granddaughter'         'grandson' 

Is it possible to have the same result but without changing the __repr__ method, because I am using it for another purpose.

EDIT:

Solution without modifying __repr__ and __str__

def other_name(self, level=0):     print '\t' * level + repr(self.value)     for child in self.children:         child.other_name(level+1) 

Answer 1

Yes, move the __repr__ code to __str__, then call str() on your tree or pass it to the print statement. Remember to use __str__ in the recursive calls too:

class node(object):     def __init__(self, value, children = []):         self.value = value         self.children = children      def __str__(self, level=0):         ret = "\t"*level+repr(self.value)+"\n"         for child in self.children:             ret += child.__str__(level+1)         return ret      def __repr__(self):         return '<tree node representation>' 

Demo:

>>> root = node('grandmother') >>> root.children = [node('daughter'), node('son')] >>> root.children[0].children = [node('granddaughter'), node('grandson')] >>> root.children[1].children = [node('granddaughter'), node('grandson')] >>> root <tree node representation> >>> str(root) "'grandmother'\n\t'daughter'\n\t\t'granddaughter'\n\t\t'grandson'\n\t'son'\n\t\t'granddaughter'\n\t\t'grandson'\n" >>> print root 'grandmother'     'daughter'         'granddaughter'         'grandson'     'son'         'granddaughter'         'grandson' 

Answer 2

Why don't you store it as a treelib object and print it out similar to how we print the CHAID tree out here with more relevant node descriptions related to your use case?

([], {0: 809, 1: 500}, (sex, p=1.47145310169e-81, chi=365.886947811, groups=[['female'], ['male']])) ├── (['female'], {0: 127, 1: 339}, (embarked, p=9.17624191599e-07, chi=24.0936494474, groups=[['C', '<missing>'], ['Q', 'S']])) │   ├── (['C', '<missing>'], {0: 11, 1: 104}, <Invalid Chaid Split>) │   └── (['Q', 'S'], {0: 116, 1: 235}, <Invalid Chaid Split>) └── (['male'], {0: 682, 1: 161}, (embarked, p=5.017855245e-05, chi=16.4413525404, groups=[['C'], ['Q', 'S']]))     ├── (['C'], {0: 109, 1: 48}, <Invalid Chaid Split>)     └── (['Q', 'S'], {0: 573, 1: 113}, <Invalid Chaid Split>)