iterators.py

def natural():
	"""A generator for all natural numbers."""
	n = 1
	while True:
		yield n
		n += 1

def fib():
	"""A generator for all Fibonacci numbers."""
	a, b = 0, 1
	while True:
		yield b
		a, b = b, a + b

def merge(iter1, iter2):
	"""Produces the sorted merge of two sorted infinite iterators."""

	left = next(iter1)
	right = next(iter2)
	while True:
		if left < right:
			yield(left)
			left = next(iter1)
		else:
			yield(right)
			right = next(iter2)

def merge3(iter1, iter2):
	"""Produces the sorted merge of two sorted iterators."""

	left = next(iter1)
	right = next(iter2)
	while True:
		if left < right:
		   yield(left)
		   try:
				left = next(iter1)
		   except StopIteration:  # iter1 is exhausted
				yield(right)
				remaining = iter2
				break
		else:
			yield(right)
			try:
				right = next(iter2)
			except StopIteration:  # iter2 is exhausted
				yield(left)
				remaining = iter1
				break
	for elem in remaining:
		yield(elem)