Enforce style check for xrange()

The following check is added in this commit:
* hacking checks for xrange()

Change-Id: If7bd8759445e5ca8cd5f4e74d91dcd02fa267904
Partial-Implements: blueprint mistral-hacking

HACKING.rst

@@ -8,3 +8,5 @@ Mistral Specific Commandments
 
 - [M318] Change assertEqual(A, None) or assertEqual(None, A) by optimal assert
   like assertIsNone(A)
+- [M327] Do not use xrange(). xrange() is not compatible with Python 3. Use
+  range() or six.moves.range() instead.

mistral/hacking/checks.py

@@ -67,6 +67,12 @@ def check_oslo_namespace_imports(logical_line):
         yield(0, msg)
 
 
+def check_python3_xrange(logical_line):
+    if re.search(r"\bxrange\s*\(", logical_line):
+        yield(0, "M327: Do not use xrange(). 'xrange()' is not compatible "
+              "with Python 3. Use range() or six.moves.range() instead.")
+
+
 class BaseASTChecker(ast.NodeVisitor):
     """Provides a simple framework for writing AST-based checks.
 

mistral/tests/unit/hacking/test_checks.py

@@ -69,6 +69,13 @@ class BaseLoggingCheckTest(base.BaseTest):
         self.assertEqual(
             len(list(checks.assert_equal_none("self.assertIsNone()"))), 0)
 
+    def test_check_python3_xrange(self):
+        func = checks.check_python3_xrange
+        self.assertEqual(1, len(list(func('for i in xrange(10)'))))
+        self.assertEqual(1, len(list(func('for i in xrange    (10)'))))
+        self.assertEqual(0, len(list(func('for i in range(10)'))))
+        self.assertEqual(0, len(list(func('for i in six.moves.range(10)'))))
+
 
 class TestLoggingWithWarn(BaseLoggingCheckTest):