A python IO class that writes to a coroutine.

coroutine_io.py

import io

class CoroutineIO(io.TextIOBase):
    """
    Creates an writable IO interface to a coroutine.
    """
    def __init__(self, coroutine):
        """
        Creates a new IO object with a coroutine. The
        coroutine should take no arguments.
        """
        self.coroutine = coroutine()
        self.coroutine.next()   # prime the pump

    def read(self):
        """
        This method isn't implemented since this is writable IO.
        """
        raise IOError('CoroutineIO is writeonly.')

    def write(self, x):
        """
        Write something to the coroutine.
        """
        self.coroutine.send(x)

def line_num_print():
    cnt = 0
    while True:
        cnt += 1
        item = (yield)
        print "%d: %s" % (cnt, item)

c = CoroutineIO(line_num_print)
c.write("Help!")
c.write("I'm trapped in python!")