diff --git a/scrapy/trunk/scrapy/core/engine.py b/scrapy/trunk/scrapy/core/engine.py
index 78e7666b5..625b34d8f 100644
--- a/scrapy/trunk/scrapy/core/engine.py
+++ b/scrapy/trunk/scrapy/core/engine.py
@@ -22,7 +22,7 @@ from scrapy.item import ScrapedItem
 from scrapy.item.pipeline import ItemPipelineManager
 from scrapy.spider import spiders
 from scrapy.spider.middleware import SpiderMiddlewareManager
-from scrapy.utils.defer import chain_deferred, defer_succeed, mustbe_deferred, deferred_degenerate
+from scrapy.utils.defer import chain_deferred, defer_succeed, mustbe_deferred, deferred_imap
 from scrapy.utils.request import request_info
 
 class ExecutionEngine(object):
@@ -255,12 +255,8 @@ class ExecutionEngine(object):
                 else:
                     log.msg("Spider must return Request, ScrapedItem or None, got '%s' while processing %s" % (type(item).__name__, request), log.WARNING, domain=domain)
 
-            class _ResultContainer(object):
-                def append(self, item):
-                    _onsuccess_per_item(item)
-
             def _onsuccess(result):
-                return deferred_degenerate(result, _ResultContainer())
+                return deferred_imap(_onsuccess_per_item, result)
 
             def _onerror(_failure):
                 if not isinstance(_failure.value, IgnoreRequest):
diff --git a/scrapy/trunk/scrapy/tests/test_utils_defer.py b/scrapy/trunk/scrapy/tests/test_utils_defer.py
new file mode 100644
index 000000000..2248c0032
--- /dev/null
+++ b/scrapy/trunk/scrapy/tests/test_utils_defer.py
@@ -0,0 +1,37 @@
+from itertools import imap
+from twisted.trial import unittest
+
+from scrapy.utils.defer import deferred_imap
+
+
+class DeferTest(unittest.TestCase):
+    def test_deferred_imap_1(self):
+        """deferred_imap storing results"""
+        seq = [1, 2, 3]
+        output = list(imap(None, seq))
+
+        dfd = deferred_imap(None, seq)
+        dfd.addCallback(self.assertEqual, output)
+        return dfd
+
+    def test_deferred_imap_2(self):
+        """deferred_imap not storing results"""
+        seq = [1, 2, 3]
+        output = list(imap(None, seq, seq))
+
+        dfd = deferred_imap(None, seq, seq)
+        dfd.addCallback(self.assertEqual, output)
+        return dfd
+
+    def test_deferred_imap_3(self):
+        """deferred_imap not storing results"""
+        seq = [1, 2, 3]
+        output = []
+        function = lambda v: output.append(v)
+
+        dfd = deferred_imap(function, seq, store_results=False)
+        dfd.addCallback(self.assertEqual, [])
+        dfd.addCallback(lambda _: self.assertEqual(output, seq))
+        return dfd
+
+
diff --git a/scrapy/trunk/scrapy/utils/defer.py b/scrapy/trunk/scrapy/utils/defer.py
index 453d7320d..1a30087f1 100644
--- a/scrapy/trunk/scrapy/utils/defer.py
+++ b/scrapy/trunk/scrapy/utils/defer.py
@@ -2,6 +2,7 @@
 Helper functions for dealing with Twisted deferreds
 """
 
+from itertools import imap
 from twisted.internet import defer, reactor
 from twisted.python import failure
 
@@ -63,19 +64,38 @@ def lambda_deferred(func):
         return d
     return deferred.addCallbacks(_success, _fail)
 
-def deferred_degenerate(generator, container=None, next_delay=0):
-    generator = iter(generator or [])
+def deferred_imap(function, *sequences, **kwargs):
+    """Analog to itertools.imap python function but friendly iterable evaluation
+    taking in count cooperative multitasking.
+
+    It returns a Deferred object that is fired when StopIteration is reached or
+    when any exception is raised when calling function.
+
+    By default the output of the evaluation is collected into a list and
+    returned as deferred result when iterable finished. But it can be disabled
+    (to save memory) using `store_results` parameter.
+
+    """
+
+    next_delay = kwargs.pop('next_delay', 0)
+    store_results = kwargs.pop('store_results', True)
+
     deferred = defer.Deferred()
-    container = container or []
+    container = []
+
+    iterator = imap(function, *sequences)
+
     def _next():
         try:
-            container.append(generator.next())
+            value = iterator.next()
+            if store_results:
+                container.append(value)
         except StopIteration:
             reactor.callLater(0, deferred.callback, container)
         except:
             reactor.callLater(0, deferred.errback, failure.Failure())
         else:
             reactor.callLater(next_delay, _next)
+
     _next()
     return deferred
-