Extend .slice() method implementation to all Iterables

Change-Id: I599019ea11a59798d131236e89ee57097b8c196e
Closes-bug: #1587509

yaql/standard_library/queries.py

@@ -452,6 +452,7 @@ def last_index_where(collection, predicate):
 @specs.parameter('length', int)
 @specs.inject('to_list', yaqltypes.Delegate('to_list', method=True))
 def slice_(collection, length, to_list):
+    collection = iter(collection)
     while True:
         res = to_list(itertools.islice(collection, length))
         if res:

yaql/tests/test_queries.py

@@ -300,6 +300,9 @@ class TestQueries(yaql.tests.TestCase):
         self.assertEqual(
             [[1, 2], [3, 4], [5]],
             self.eval('range(1, 6).slice(2)'))
+        self.assertEqual(
+            [[1, 2], [3, 4], [5]],
+            self.eval('[1,2,3,4,5].slice(2)'))
 
     def test_split(self):
         self.assertEqual(