adding to_list() util and test

--HG--
extra : convert_revision : svn%3Ab85faa78-f9eb-468e-a121-7cced6da292c%40898

scrapy/trunk/scrapy/tests/test_utils_misc.py

@@ -1,7 +1,7 @@
 import unittest
 from cStringIO import StringIO
 
-from scrapy.utils.misc import hash_values, items_to_csv, load_object
+from scrapy.utils.misc import hash_values, items_to_csv, load_object, to_list
 from scrapy.core.exceptions import UsageError
 from scrapy.item import ScrapedItem
 
@@ -60,5 +60,10 @@ class UtilsMiscTestCase(unittest.TestCase):
         obj = load_object('scrapy.utils.misc.load_object')
         assert obj is load_object
 
+    def test_to_list(self):
+        self.assertEqual(to_list(None), [])
+        self.assertEqual(to_list('lala'), ['lala'])
+        self.assertEqual(to_list(('lala', 'poo')), ['lala', 'poo'])
+
 if __name__ == "__main__":
     unittest.main()

scrapy/trunk/scrapy/utils/misc.py

@@ -15,6 +15,14 @@ from scrapy.utils.python import flatten, unicode_to_str
 from scrapy.utils.markup import remove_entities
 from scrapy.utils.defer import defer_succeed
 
+def to_list(obj):
+    if obj is None:
+        return []
+    elif hasattr(obj, '__iter__'):
+        return list(obj)
+    else:
+        return [obj]
+
 def dict_updatedefault(D, E, **F):
     """
     updatedefault(D, E, **F) -> None.