Add VerNum.__index__() for Python 3 support

On Python 3, some functions like range() don't try to call the __int__()
method to cast an object to integer, but try instead the __index__()
method.

Add an __index__() method to mimick correctly the int type on Python 3.

Change-Id: I8df116d80e201778714a59367600eaef644266ed

2 files changed, 10 insertions, 0 deletions

diff --git a/migrate/tests/versioning/test_version.py b/migrate/tests/versioning/test_version.py
index 00ce695..df50072 100644
--- a/migrate/tests/versioning/test_version.py
+++ b/migrate/tests/versioning/test_version.py
@@ -69,6 +69,13 @@ class TestVerNum(fixture.Base):
         self.assertTrue(VerNum(2) >= 1)
         self.assertFalse(VerNum(1) >= 2)
 
+    def test_int_cast(self):
+        ver = VerNum(3)
+        # test __int__
+        self.assertEqual(int(ver), 3)
+        # test __index__: range() doesn't call __int__
+        self.assertEqual(list(range(ver, ver)), [])
+
 
 class TestVersion(fixture.Pathed):
 
diff --git a/migrate/versioning/version.py b/migrate/versioning/version.py
index de7008f..3ab814c 100644
--- a/migrate/versioning/version.py
+++ b/migrate/versioning/version.py
@@ -65,6 +65,9 @@ class VerNum(object):
     def __int__(self):
         return int(self.value)
 
+    def __index__(self):
+        return int(self.value)
+
     if six.PY3:
         def __hash__(self):
             return hash(self.value)