Printing a Tree data structure in Python

72,019

Solution 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'

Solution 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>)
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Kristof Pal
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Kristof Pal

Updated on July 09, 2022

Comments

  • Kristof Pal
    Kristof Pal almost 2 years

    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)