Python Trie implementation

trie.py

#!/usr/bin/env python

class Node(object):

    __slots__ = ('letters', 'children', 'num_occurs')

    def __init__(self, letters=None):

        self.letters = letters # only leaf nodes have non-None letters
        self.children = {}
        self.num_occurs = 0


class Trie(object):
    """This implementation of trie has no path compression
    """

    def __init__(self):
        self.root = Node()

    def insert(self, word):
        node = self.root
        node.num_occurs += 1
        for letter in word:
            if letter not in node.children:
                node.children[letter] = Node()
            node = node.children[letter]
            node.num_occurs += 1
        else:
            node.letters = word

    def find(self, word):
        node = self.root
        for letter in word:
            if letter in node.children:
                node = node.children[letter]
            else:
                return None
        else:
            return node