iteratee with python generator

def generator(fun):
    def wrapper(*args, **kwargs):
        gen = fun(*args, **kwargs)
        gen.next()
        return gen
    return wrapper

@generator
def identity():
    chunk = None
    while True:
        chunk = yield chunk

@generator
def lineno():
    lineno = 0
    chunk = yield
    while True:
        lineno += 1
        chunk = yield lineno

@generator
def lastn(n):
    buf = []
    chunk = yield
    while True:
        buf.append(chunk)
        if len(buf)>n:
            buf.pop(0)
        chunk = yield buf

@generator
def grepw(word):
    line = yield
    while True:
        if word in line.split():
            line = yield line
        else:
            line = yield

@generator
def split(*gens):
    chunk = yield
    while True:
        buf = []
        for g in gens:
            buf.append( g.send(chunk) )
        if None in buf:
            chunk = yield
        else:
            chunk = yield buf

@generator
def pair(*gens):
    chunks = yield
    while True:
        buf = []
        for chunk, gen in zip(chunks, gens):
            buf.append( gen.send(chunk) )
        if None in buf:
            chunk = yield
        else:
            chunks = yield buf

@generator
def chain(g1, g2):
    chunk = yield
    while True:
        chunk = g1.send(chunk)
        if chunk:
            chunk = yield g2.send(chunk)
        else:
            chunk = yield

def feed(enum, gen):
    for trunk in enum:
        result = gen.send(trunk)
        if result!=None:
            yield result

if __name__ == '__main__':
    import sys
    word = sys.argv[1]
    count = int(sys.argv[2])
    enum = open(sys.argv[3])
    '''
           +- lineno --------+
           |                 |
    line --+- grepw    ------+--- (lineno, line, context lines)
           |                 |
           +- context lines -+
    '''
    gen = split(
              lineno(),
              grepw(word),
              lastn(count)
          )

    res = feed(enum, gen)
    for (lineno, line, last) in res:
        print lineno
        print ''.join(last)