OrderedSet for Python 2.7

While working on the Kosaraju algorithm for Coursera course [1] homework, I wrote a simple and (hopefully) convenient OrderedSet for Python 2.7

Feel free to use and share it:

	from collections import OrderedDict
	class OrderedSet(OrderedDict):
	def pop(self):
	""" Returns and removes last element of the set """
	if not self:
	raise KeyError('dictionary is empty')
	key = next(reversed(self))
	del self[key]
	return key
	def peek(self):
	""" Returns last element of the set without removing it """
	if not self:
	raise KeyError('dictionary is empty')
	key = next(reversed(self))
	return key
	def at(self, i):
	""" Returns element at the index """
	if not self:
	raise KeyError('dictionary is empty')
	return list(self)[i]
	def extend(self, iterable):
	""" Extends OrderedList by appending elements from the iterable """
	for element in iterable:
	if element not in self:
	self[element] = True
	def append(self, element):
	""" Appends an element to the end of the ordered set """
	if element not in self:
	self[element] = True

view raw ordered_set.py hosted with ❤ by GitHub

And just in case you are looking for unit tests or simple usage examples, please refer to the gist below:

	def test_ordered_set_a():
	o_s = OrderedSet()
	SIZE = 100
	for i in range(SIZE):
	o_s.append(i)
	for i in range(SIZE * 2):
	assert o_s.peek() == SIZE - 1
	for i in range(SIZE):
	assert o_s.pop() == SIZE - 1 - i
	assert len(o_s) == 0
	just_a_list = [i for i in range(SIZE)]
	o_s.extend(just_a_list)
	for i in range(SIZE):
	assert o_s.at(i) == i
	o_s.extend(just_a_list)
	assert len(o_s) == SIZE
	for i in range(SIZE):
	assert o_s.at(i) == i
	just_a_list = [i for i in range(SIZE / 2, SIZE * 2)]
	o_s.extend(just_a_list)
	assert len(o_s) == SIZE * 2
	for i in range(SIZE * 2):
	assert o_s.at(i) == i

view raw test_ordered_set.py hosted with ❤ by GitHub

Cheers!

[1] Algorithms: Design and Analysis, Part 1
https://class.coursera.org/algo-004/class/index