"tail -f" style file-reading in Twisted

blam.py

#!/usr/bin/env python

import sys
from twisted.internet.interfaces import IReadDescriptor
from twisted.internet.fdesc import setNonBlocking
from twisted.internet import reactor
from zope.interface import implementer

@implementer(IReadDescriptor)
class Blam(object):
    def __init__(self, f):
        self.file = f
        setNonBlocking(self.file)

    def logPrefix(self):
        return 'blam'

    def doRead(self):
        data = self.file.read()
        if data:
            print "it's dataz", data

    def fileno(self):
        return self.file.fileno()

    def connectionLost(self, why):
        print "closed", why

f = Blam(open(sys.argv[1], 'r'))
reactor.addReader(f)
print "go!", sys.argv[1]
reactor.run()

does not notice new lines on OSX
uses 100% cpu

Hmm, it seems to be using 100% CPU on Debian, also -- clearly something is missing...