Allow passing Python objects to middleware dict settings

scrapy/middleware.py

@@ -1,4 +1,5 @@
 from collections import defaultdict
+from inspect import isclass
 import logging
 import pprint
 
@@ -31,7 +32,9 @@ class MiddlewareManager(object):
         for clspath in mwlist:
             try:
                 mwcls = load_object(clspath)
-                if crawler and hasattr(mwcls, 'from_crawler'):
+                if not isclass(mwcls):
+                    mw = mwcls
+                elif crawler and hasattr(mwcls, 'from_crawler'):
                     mw = mwcls.from_crawler(crawler)
                 elif hasattr(mwcls, 'from_settings'):
                     mw = mwcls.from_settings(settings)

scrapy/utils/misc.py

@@ -31,10 +31,15 @@ def arg_to_iter(arg):
 def load_object(path):
     """Load an object given its absolute object path, and return it.
 
-    object can be a class, function, variable o instance.
+    If ``path`` is not a string, it will be returned.
+
+    The object can be a class, function, variable, or instance.
     path ie: 'scrapy.downloadermiddlewares.redirect.RedirectMiddleware'
     """
 
+    if not isinstance(path, six.string_types):
+        return path
+
     try:
         dot = path.rindex('.')
     except ValueError:

tests/test_middleware.py

@@ -91,3 +91,16 @@ class MiddlewareManagerTest(unittest.TestCase):
         mwman = TestMiddlewareManager.from_settings(settings)
         classes = [x.__class__ for x in mwman.middlewares]
         self.assertEqual(classes, [M1, M3])
+
+    def test_instances_from_settings(self):
+        settings = Settings()
+        myM3 = M3()
+        class InstanceTestMiddlewareManager(MiddlewareManager):
+            @classmethod
+            def _get_mwlist_from_settings(cls, settings):
+                return [ 'tests.test_middleware.M1', M2, myM3 ]
+        mwman = InstanceTestMiddlewareManager.from_settings(settings)
+        self.assertIsInstance(mwman.middlewares[0], M1)
+        self.assertIsInstance(mwman.middlewares[1], M2)
+        self.assertIs(mwman.middlewares[2], myM3)
+

tests/test_utils_misc/__init__.py

@@ -11,7 +11,9 @@ class UtilsMiscTestCase(unittest.TestCase):
 
     def test_load_object(self):
         obj = load_object('scrapy.utils.misc.load_object')
-        assert obj is load_object
+        self.assertIs(obj, load_object)
+        not_a_string = int(1000)
+        self.assertIs(load_object(not_a_string), not_a_string)
         self.assertRaises(ImportError, load_object, 'nomodule999.mod.function')
         self.assertRaises(NameError, load_object, 'scrapy.utils.misc.load_object999')