How can I implement a tree in Python?
I recommend anytree (I am the author).
from anytree import Node, RenderTreeudo = Node("Udo")marc = Node("Marc", parent=udo)lian = Node("Lian", parent=marc)dan = Node("Dan", parent=udo)jet = Node("Jet", parent=dan)jan = Node("Jan", parent=dan)joe = Node("Joe", parent=dan)print(udo)Node('/Udo')print(joe)Node('/Udo/Dan/Joe')for pre, fill, node in RenderTree(udo): print("%s%s" % (pre, node.name))Udo├── Marc│ └── Lian└── Dan ├── Jet ├── Jan └── Joeprint(dan.children)(Node('/Udo/Dan/Jet'), Node('/Udo/Dan/Jan'), Node('/Udo/Dan/Joe'))
anytree has also a powerful API with:
- simple tree creation
- simple tree modification
- pre-order tree iteration
- post-order tree iteration
- resolve relative and absolute node paths
- walking from one node to an other.
- tree rendering (see example above)
- node attach/detach hookups
Python doesn't have the quite the extensive range of "built-in" data structures as Java does. However, because Python is dynamic, a general tree is easy to create. For example, a binary tree might be:
class Tree: def __init__(self): self.left = None self.right = None self.data = None
You can use it like this:
root = Tree()root.data = "root"root.left = Tree()root.left.data = "left"root.right = Tree()root.right.data = "right"
If you need an arbitrary number of children per node, then use a list of children:
class Tree: def __init__(self, data): self.children =  self.data = dataleft = Tree("left")middle = Tree("middle")right = Tree("right")root = Tree("root")root.children = [left, middle, right]
A generic tree is a node with zero or more children, each one a proper (tree) node. It isn't the same as a binary tree, they're different data structures, although both shares some terminology.
There isn't any builtin data structure for generic trees in Python, but it's easily implemented with classes.
class Tree(object): "Generic tree node." def __init__(self, name='root', children=None): self.name = name self.children =  if children is not None: for child in children: self.add_child(child) def __repr__(self): return self.name def add_child(self, node): assert isinstance(node, Tree) self.children.append(node)# *# /|\# 1 2 +# / \# 3 4t = Tree('*', [Tree('1'), Tree('2'), Tree('+', [Tree('3'), Tree('4')])])