* implemented Tom's nice config string for the trotlle rate e.g. '3/sec'

* We now have per-user, per-view and per-resource throttling

* Added a new exxception class as a convenience to detect pointless throttles

* refactored

djangorestframework/permissions.py

@@ -29,6 +29,10 @@ _503_THROTTLED_RESPONSE = ErrorResponse(
     {'detail': 'request was throttled'})
 
 
+class ConfigurationException(BaseException):
+        """To alert for bad configuration desicions as a convenience."""
+        pass
+
 
 class BasePermission(object):
     """
@@ -87,70 +91,83 @@ class IsUserOrIsAnonReadOnly(BasePermission):
             self.view.method != 'HEAD'):
             raise _403_FORBIDDEN_RESPONSE
 
-
-class PerUserThrottling(BasePermission):
+class BaseThrottle(BasePermission):
     """
-    Rate throttling of requests on a per-user basis.
+    Rate throttling of requests.
 
     The rate (requests / seconds) is set by a :attr:`throttle` attribute on the ``View`` class.
-    The attribute is a two tuple of the form (number of requests, duration in seconds).
-
-    The user id will be used as a unique identifier if the user is authenticated.
-    For anonymous requests, the IP address of the client will be used.
+    The attribute is a string of the form 'number of requests/period'. Period must be an element
+    of (sec, min, hour, day)
 
     Previous request information used for throttling is stored in the cache.
     """    
 
-    def check_permission(self, user):
-        (num_requests, duration) = getattr(self.view, 'throttle', (0, 0))
-        
-        if user.is_authenticated():
-            ident = str(user)
-        else:
-            ident = self.view.request.META.get('REMOTE_ADDR', None)
+    def get_cache_key(self):
+        """Should return the cache-key corresponding to the semantics of the class that implements
+        the throttling behaviour. 
+        """
+        pass
 
-        key = 'throttle_%s' % ident
-        history = cache.get(key, [])
-        now = time.time()
+    def check_permission(self, auth):
+        num, period = getattr(self.view, 'throttle', '0/sec').split('/')
+        self.num_requests = int(num)
+        self.duration = {'s': 1, 'm': 60, 'h': 3600, 'd': 86400}[period[0]]
+        self.auth = auth
+        self.check_throttle()
+        
+    def check_throttle(self):
+        """On success calls `throttle_success`. On failure calls `throttle_failure`. """
+        self.key = self.get_cache_key()
+        self.history = cache.get(self.key, [])
+        self.now = time.time()
         
         # Drop any requests from the history which have now passed the throttle duration
-        while history and history[0] < now - duration:
-            history.pop()
-
-        if len(history) >= num_requests:
-            raise _503_THROTTLED_RESPONSE
+        while self.history and self.history[0] < self.now - self.duration:
+            self.history.pop()
 
-        history.insert(0, now)
-        cache.set(key, history, duration)
+        if len(self.history) >= self.num_requests:
+            self.throttle_failure()
+        else:
+            self.throttle_success()
     
-class PerResourceThrottling(BasePermission):
-    """
-    Rate throttling of requests on a per-resource basis.
+    def throttle_success(self):
+        """Inserts the current request's timesatmp along with the key into the cache."""
+        self.history.insert(0, self.now)
+        cache.set(self.key, self.history, self.duration)
     
-    The rate (requests / seconds) is set by a :attr:`throttle` attribute on the ``View`` class.
-    The attribute is a two tuple of the form (number of requests, duration in seconds).
+    def throttle_failure(self):
+        """Raises a 503 """
+        raise _503_THROTTLED_RESPONSE
     
+class PerUserThrottling(BaseThrottle):
+    """
     The user id will be used as a unique identifier if the user is authenticated.
     For anonymous requests, the IP address of the client will be used.
-
-    Previous request information used for throttling is stored in the cache.
     """
 
-    def check_permission(self, ignore):
-        (num_requests, duration) = getattr(self.view, 'throttle', (0, 0))
-        
-        
-        key = 'throttle_%s' % self.view.__class__.__name__
+    def get_cache_key(self):
+        if self.auth.is_authenticated():
+            ident = str(self.auth)
+        else:
+            ident = self.view.request.META.get('REMOTE_ADDR', None)
+        return 'throttle_%s' % ident
 
-        history = cache.get(key, [])
-        now = time.time()
+class PerViewThrottling(BaseThrottle):
+    """
+    The class name of the cuurent view will be used as a unique identifier.
+    """
 
-        # Drop any requests from the history which have now passed the throttle duration
-        while history and history[0] < now - duration:
-            history.pop()
+    def get_cache_key(self):
+        return 'throttle_%s' % self.view.__class__.__name__
     
-        if len(history) >= num_requests:
-            raise _503_THROTTLED_RESPONSE
+class PerResourceThrottling(BaseThrottle):
+    """
+    The class name of the cuurent resource will be used as a unique identifier.
+    Raises :exc:`ConfigurationException` if no resource attribute is set on the view class.
+    """
 
-        history.insert(0, now)
-        cache.set(key, history, duration)
+    def get_cache_key(self):
+        if self.view.resource != None:
+            return 'throttle_%s' % self.view.resource.__class__.__name__
+        raise ConfigurationException(
+            "A per-resource throttle was set to a view that does not have a resource.")
\ No newline at end of file