Task context: implement comparison operators

__cmp__ is no longer used in python3

Other operators need to be defined instead.

https://docs.python.org/3/whatsnew/3.0.html#ordering-comparisons
"The cmp() function should be treated as gone, and the __cmp__() special
method is no longer supported. Use __lt__() for sorting, __eq__() with
__hash__(), and other rich comparisons as needed. (If you really need
the cmp() functionality, you could use the expression (a > b) - (a < b)
as the equivalent for cmp(a, b).)"

https://www.python.org/dev/peps/pep-0207/

This change does it based on get_order and class meta properties.

Downstream projects that rely on context comparison (such as
rally-openstack) will benefit from this change.

Change-Id: I4991acccefd4754e209feafd5e24d03c76c283f8
Depends-On: I42db6045ae88c34d3576beb737bb7e955c5f2132
Needed-By: I6bb31fe1d3f79a8fd4707a5576204dee69a3f307
Partial-Bug: #1819274

rally/task/context.py

@@ -168,6 +168,21 @@ class BaseContext(plugin.Plugin, functional.FunctionalMixin,
     def __exit__(self, exc_type, exc_value, exc_traceback):
         self.cleanup()
 
+    def __eq__(self, other):
+        return self.get_order() == other.get_order()
+
+    def __lt__(self, other):
+        return self.get_order() < other.get_order()
+
+    def __gt__(self, other):
+        return self.get_order() > other.get_order()
+
+    def __le__(self, other):
+        return self.get_order() <= other.get_order()
+
+    def __ge__(self, other):
+        return self.get_order() >= other.get_order()
+
 
 @validation.add_default("jsonschema")
 @plugin.base()

tests/unit/task/test_context.py

@@ -118,6 +118,63 @@ class BaseContextTestCase(test.TestCase):
         ins = fakes.FakeContext(ctx)
         self.assertEqual("foo_uuid", ins.get_owner_id())
 
+    def test___eq__(self):
+        @context.configure(name="bar", order=1)
+        class BarContext(fakes.FakeContext):
+            pass
+
+        foo_context = fakes.FakeContext()
+        bar_context = BarContext()
+        self.assertTrue(foo_context == bar_context)
+
+    def test___lt__(self):
+        @context.configure(name="barlt", order=2)
+        class BarContext(fakes.FakeContext):
+            pass
+
+        foo_context = fakes.FakeContext()
+        bar_context = BarContext()
+        self.assertTrue(foo_context < bar_context)
+
+    def test___gt__(self):
+        @context.configure(name="bargt", order=0)
+        class BarContext(fakes.FakeContext):
+            pass
+
+        foo_context = fakes.FakeContext()
+        bar_context = BarContext()
+        self.assertTrue(foo_context > bar_context)
+
+    def test___le__(self):
+        @context.configure(name="barle", order=1)
+        class BarContext(fakes.FakeContext):
+            pass
+
+        @context.configure(name="bazle", order=2)
+        class BazContext(fakes.FakeContext):
+            pass
+
+        foo_context = fakes.FakeContext()
+        bar_context = BarContext()
+        baz_context = BazContext()
+        self.assertTrue(foo_context <= bar_context)
+        self.assertTrue(foo_context <= baz_context)
+
+    def test___ge__(self):
+        @context.configure(name="barge", order=0)
+        class BarContext(fakes.FakeContext):
+            pass
+
+        @context.configure(name="bazge", order=-1)
+        class BazContext(fakes.FakeContext):
+            pass
+
+        foo_context = fakes.FakeContext()
+        bar_context = BarContext()
+        baz_context = BazContext()
+        self.assertTrue(foo_context >= bar_context)
+        self.assertTrue(foo_context >= baz_context)
+
 
 class ContextManagerTestCase(test.TestCase):
     @mock.patch("rally.task.context.ContextManager._get_sorted_context_lst")