diff --git a/eventlet/api.py b/eventlet/api.py
index 95c1ae8..4ff0bc3 100644
--- a/eventlet/api.py
+++ b/eventlet/api.py
@@ -150,9 +150,9 @@ def trampoline(fd, read=None, write=None, timeout=None, timeout_exc=TimeoutError
         t = hub.schedule_call_global(timeout, current.throw, timeout_exc)
     try:
         if read:
-            listener = hub.add("read", fileno, cb)
+            listener = hub.add(hub.READ, fileno, cb)
         if write:
-            listener = hub.add("write", fileno, cb)
+            listener = hub.add(hub.WRITE, fileno, cb)
         try:
             return hub.switch()
         finally:
@@ -206,9 +206,9 @@ def select(read_list, write_list, error_list, timeout=None):
     try:
         for k, v in ds.iteritems():
             if v.get('read'):
-                hub.add('read', k, on_read)
+                hub.add(hub.READ, k, on_read)
             if v.get('write'):
-                hub.add_writer('write', k, on_write)
+                hub.add(hub.WRITE, k, on_write)
             descriptors.append(k)
         try:
             return hub.switch()
diff --git a/eventlet/hubs/hub.py b/eventlet/hubs/hub.py
index 3479df7..6da9a9f 100644
--- a/eventlet/hubs/hub.py
+++ b/eventlet/hubs/hub.py
@@ -25,9 +25,12 @@ import time
 from eventlet.support import greenlets as greenlet
 from eventlet.timer import Timer, LocalTimer
 
+READ="read"
+WRITE="write"
+
 class FdListener(object):
     def __init__(self, evtype, fileno, cb):
-        assert (evtype == 'read' or evtype == 'write')
+        assert (evtype is READ or evtype is WRITE)
         self.evtype = evtype
         self.fileno = fileno
         self.cb = cb
@@ -54,9 +57,12 @@ class BaseHub(object):
     specific to a particular underlying event architecture. """
 
     SYSTEM_EXCEPTIONS = (KeyboardInterrupt, SystemExit)
+    
+    READ = READ
+    WRITE = WRITE
 
     def __init__(self, clock=time.time):
-        self.listeners = {'read':{}, 'write':{}}
+        self.listeners = {READ:{}, WRITE:{}}
         self.closed_fds = []
 
         self.clock = clock
@@ -78,7 +84,7 @@ class BaseHub(object):
     def add(self, evtype, fileno, cb):
         """ Signals an intent to or write a particular file descriptor.
 
-        The *evtype* argument is either the string 'read' or the string 'write'.
+        The *evtype* argument is either the constant READ or WRITE.
 
         The *fileno* argument is the file number of the file of interest.
 
@@ -106,8 +112,8 @@ class BaseHub(object):
         
     def remove_descriptor(self, fileno):
         """ Completely remove all listeners for this fileno."""
-        self.listeners['read'].pop(fileno, None)
-        self.listeners['write'].pop(fileno, None)
+        self.listeners[READ].pop(fileno, None)
+        self.listeners[WRITE].pop(fileno, None)
 
     def stop(self):
         self.abort()
@@ -304,10 +310,10 @@ class BaseHub(object):
     # for debugging:
 
     def get_readers(self):
-        return self.listeners['read']
+        return self.listeners[READ]
 
     def get_writers(self):
-        return self.listeners['write']
+        return self.listeners[WRITE]
 
     def get_timers_count(hub):
         return max(len(x) for x in [hub.timers, hub.next_timers])
diff --git a/eventlet/hubs/libevent.py b/eventlet/hubs/libevent.py
index bd328dc..ef94cc8 100644
--- a/eventlet/hubs/libevent.py
+++ b/eventlet/hubs/libevent.py
@@ -24,7 +24,7 @@ import traceback
 import event
 
 from eventlet import api
-from eventlet.hubs.hub import BaseHub, FdListener
+from eventlet.hubs.hub import BaseHub, FdListener, READ, WRITE
 
 
 class event_wrapper(object):
@@ -129,9 +129,9 @@ class Hub(BaseHub):
     running = property(_getrunning, _setrunning)
 
     def add(self, evtype, fileno, cb):
-        if evtype == 'read':
+        if evtype is READ:
             evt = event.read(fileno, cb, fileno)
-        elif evtype == 'write':
+        elif evtype is WRITE:
             evt = event.write(fileno, cb, fileno)
             
         listener = FdListener(evtype, fileno, evt)
@@ -179,12 +179,6 @@ class Hub(BaseHub):
         self.events_to_add.append(wrapper)
         return wrapper
         
-    def get_readers(self):
-        return self.listeners['read']
-
-    def get_writers(self):
-        return self.listeners['write']
-
     def _version_info(self):
         baseversion = event.__version__
         return baseversion
diff --git a/eventlet/hubs/poll.py b/eventlet/hubs/poll.py
index a84a572..fda0f78 100644
--- a/eventlet/hubs/poll.py
+++ b/eventlet/hubs/poll.py
@@ -26,13 +26,13 @@ import errno
 from time import sleep
 import time
 
-from eventlet.hubs import hub
+from eventlet.hubs.hub import BaseHub, READ, WRITE
 
 EXC_MASK = select.POLLERR | select.POLLHUP
 READ_MASK = select.POLLIN
 WRITE_MASK = select.POLLOUT
 
-class Hub(hub.BaseHub):
+class Hub(BaseHub):
     def __init__(self, clock=time.time):
         super(Hub, self).__init__(clock)
         self.poll = select.poll()
@@ -52,9 +52,9 @@ class Hub(hub.BaseHub):
 
     def register(self, fileno):
         mask = 0
-        if self.listeners['read'].get(fileno):
+        if self.listeners[READ].get(fileno):
             mask |= READ_MASK
-        if self.listeners['write'].get(fileno):
+        if self.listeners[WRITE].get(fileno):
             mask |= WRITE_MASK
         if mask:
             self.poll.register(fileno, mask)
@@ -72,8 +72,8 @@ class Hub(hub.BaseHub):
             pass
 
     def wait(self, seconds=None):
-        readers = self.listeners['read']
-        writers = self.listeners['write']
+        readers = self.listeners[READ]
+        writers = self.listeners[WRITE]
 
         if not readers and not writers:
             if seconds:
diff --git a/eventlet/hubs/selects.py b/eventlet/hubs/selects.py
index e6354a9..dcfde51 100644
--- a/eventlet/hubs/selects.py
+++ b/eventlet/hubs/selects.py
@@ -23,9 +23,9 @@ import select
 import errno
 import time
 
-from eventlet.hubs import hub
+from eventlet.hubs.hub import BaseHub, READ, WRITE
 
-class Hub(hub.BaseHub):
+class Hub(BaseHub):
     def _remove_closed_fds(self):
         """ Iterate through fds that have had their socket objects recently closed,
         removing the ones that are actually closed per the operating system.
@@ -38,8 +38,8 @@ class Hub(hub.BaseHub):
                     self.remove_descriptor(fd)
 
     def wait(self, seconds=None):
-        readers = self.listeners['read']
-        writers = self.listeners['write']
+        readers = self.listeners[READ]
+        writers = self.listeners[WRITE]
         if not readers and not writers:
             if seconds:
                 time.sleep(seconds)
diff --git a/eventlet/hubs/twistedr.py b/eventlet/hubs/twistedr.py
index a54da0d..93ed454 100644
--- a/eventlet/hubs/twistedr.py
+++ b/eventlet/hubs/twistedr.py
@@ -23,7 +23,7 @@ import sys
 import threading
 from twisted.internet.base import DelayedCall as TwistedDelayedCall
 from eventlet import api
-from eventlet.hubs import hub
+from eventlet.hubs.hub import FdListener, READ, WRITE
 
 
 class DelayedCall(TwistedDelayedCall):
@@ -74,11 +74,11 @@ class socket_rwdescriptor(hub.FdListener):
     disconnected = False
 
     def doRead(self):
-        if self.evtype == 'read':
+        if self.evtype is READ:
             self.cb(self)
 
     def doWrite(self):
-        if self.evtype == 'write':
+        if self.evtype == WRITE:
             self.cb(self)
 
     def connectionLost(self, reason):
@@ -130,9 +130,9 @@ class BaseTwistedHub(object):
     def add(self, evtype, fileno, cb):
         from twisted.internet import reactor
         descriptor = socket_rwdescriptor(evtype, fileno, cb)
-        if evtype == 'read':
+        if evtype is READ:
             reactor.addReader(descriptor)
-        if evtype == 'write':
+        if evtype is WRITE:
             reactor.addWriter(descriptor)
         return descriptor