gistfile1.txt

from functools import partial
import time

def coroutine(func):
	def start(*args,**kwargs):
		cr = func(*args,**kwargs)
		cr.next()
		return cr
	return start

def follow(target, f):
	f.seek(0,2)      # Go to the end of the file
	while True:
		line = f.readline()
		if not line:
			time.sleep(0.1)    # Sleep briefly
			continue
		target.send(line)

@coroutine
def grep(target, pattern):
	while True:
		line = (yield)           # Receive a line
		if pattern in line:
			target.send(line)    # Send to next stage

@coroutine
def printer():
	while True:
		line = (yield)
		print line,

def pipe(*args):
	def run(input_func, func=None):
		print 'run', input_func, func
		if isinstance(input_func, tuple):
			data = list(input_func)
			input_func = data.pop(0)
			return input_func(func, *data)
		else:
			if func:
				return input_func(func)
			else:
				return input_func()

	args = list(args)
	
	source = args.pop(0)
	sink = args.pop(len(args)-1)

	func = run(sink)

	for arg in args[::-1]:
		func = run(arg, func)

	return run(source, func)

pipe((follow,open('example.txt')),(grep,'pattern'),printer)