use function next() instead of next() method on iterator objects

Python 3 introduced a next() function to replace the next() method on
iterator objects. Rather than calling the method on the iterator, the next()
function is called with the iterable object as it's sole parameter, which
calls the underlying __next__() method.

The next() function was backported to Python 2.6 which allows us to use either
the 2.x or 3.x way simultaneously.

Change-Id: I945225b1b0c6c39842a77f4a136e9431b798229f
Closes-Bug: #1403074

tests/hacking/README.rst

@@ -29,4 +29,5 @@ Rally Specific Commandments
  * [N334] - Ensure that ``itertools.imap`` is not used
  * [N335] - Ensure that ``xrange`` is not used
  * [N336] - Ensure that ``string.lowercase`` and ``string.uppercase`` are not used
+ * [N337] - Ensure that ``next()`` method on iterator objects is not used
 * [N340] - Ensure that we are importing always ``from rally import objects``

tests/hacking/checks.py

@@ -53,6 +53,7 @@ re_itertools_imap_method = re.compile(r"(^|[\s=])itertools\.imap\(")
 re_xrange_method = re.compile(r"(^|[\s=])xrange\(")
 re_string_lower_upper_case_method = re.compile(
     r"(^|[(,\s=])string\.(lower|upper)case([)\[,\s]|$)")
+re_next_on_iterator_method = re.compile(r"\.next\(\)")
 
 
 def _parse_assert_mock_str(line):
@@ -322,6 +323,21 @@ def check_string_lower_upper_case_method(logical_line):
                   "rather than string.lowercase or string.uppercase.")
 
 
+def check_next_on_iterator_method(logical_line):
+    """Check if next() method on iterator objects are properly called
+
+    Python 3 introduced a next() function to replace the next() method on
+    iterator objects. Rather than calling the method on the iterator,
+    the next() function is called with the iterable object as it's sole
+    parameter, which calls the underlying __next__() method.
+
+    N337
+    """
+    res = re_next_on_iterator_method.search(logical_line)
+    if res:
+        yield (0, "N337: Use next(iterator) rather than iterator.next().")
+
+
 def check_no_direct_rally_objects_import(logical_line, filename):
     """Check if rally.objects are properly imported.
 
@@ -356,4 +372,5 @@ def factory(register):
     register(check_itertools_imap_method)
     register(check_xrange_method)
     register(check_string_lower_upper_case_method)
+    register(check_next_on_iterator_method)
     register(check_no_direct_rally_objects_import)

tests/unit/test_hacking.py

@@ -176,6 +176,13 @@ class HackingTestCase(test.TestCase):
         self.assertEqual(len(list(checks.check_string_lower_upper_case_method(
             "string.ascii_uppercase[:16]"))), 0)
 
+    def test_check_next_on_iterator_method(self):
+        self.assertEqual(len(list(checks.check_next_on_iterator_method(
+            "iterator.next()"))), 1)
+
+        self.assertEqual(len(list(checks.check_next_on_iterator_method(
+            "next(iterator)"))), 0)
+
     def test_assert_equal_none(self):
         self.assertEqual(len(list(checks.assert_equal_none(
             "self.assertEqual(A, None)"))), 1)