#!/usr/bin/python

from math import sqrt, atan2, pi, sin, cos, floor
from random import randint

class Node:
	def __init__(self, name=None, parent=None):
		self._name = name
		self._parent = parent
		self._child = {}

	def newChild(self, name):
		_child[name] = Node(name=name, parent=self)
		
	def children(self):
		return self._child.values()

	def child_names(self):
		return self._child.keys()

	def child(self, name):
		return self._child[name]

	def parent(self):
		return self._parent

	def name(self):
		return self.name

class Arc:
	def __init__(self, fromNode, toNode, name=None):
		self.fromNode = fromNode
		self.toNode = toNode

	def other(self, node):
		if node == self.fromNode:
			return self.toNode
		if node == self.toNode:
			return self.fromNode
		raise Exception, 'Node is not attached to this Arc'
		# should use a subclass of Exception?

a = Node()
b = Node()
c = Node()
arc = Arc(a, b)

if arc.other(a) == b: print 'yes, working'
if arc.other(b) == a: print 'yes, working'