Python2: Fix metaclass, super() and OrderedMeta

* Add six dependency
* Replace "metaclass=" syntax with six.with_metaclass()
* Add parameters to super()
* Only define OrderedMeta on Python 3

Related-Bug: 1726399
Change-Id: I21800320ef23cc95fc07278864e73b64bb7d6d08

ospurge/resources/base.py

@@ -19,6 +19,7 @@ try:
     import funcsigs as inspect   # Python 2.7
 except ImportError:
     import inspect
+import six
 
 from ospurge import exceptions
 
@@ -30,7 +31,7 @@ if TYPE_CHECKING:  # pragma: no cover
 
 class MatchSignaturesMeta(type):
     def __init__(self, clsname, bases, clsdict):
-        super().__init__(clsname, bases, clsdict)
+        super(MatchSignaturesMeta, self).__init__(clsname, bases, clsdict)
         sup = super(self, self)  # type: ignore   # See python/mypy #857
         for name, value in clsdict.items():
             if name.startswith('_') or not callable(value):
@@ -47,37 +48,43 @@ class MatchSignaturesMeta(type):
                                     value_name, prev_sig, val_sig)
 
 
-class OrderedMeta(type):
-    def __new__(cls, clsname, bases, clsdict):
-        ordered_methods = cls.ordered_methods
-        allowed_next_methods = list(ordered_methods)
-        for name, value in clsdict.items():
-            if name not in ordered_methods:
-                continue
+if six.PY3:
+    class OrderedMeta(type):
+        def __new__(cls, clsname, bases, clsdict):
+            ordered_methods = cls.ordered_methods
+            allowed_next_methods = list(ordered_methods)
+            for name, value in clsdict.items():
+                if name not in ordered_methods:
+                    continue
 
-            if name not in allowed_next_methods:
-                value_name = getattr(value, '__qualname__', value.__name__)
-                logging.warning(
-                    "Method %s not defined at the correct location. Methods "
-                    "in class %s must be defined in the following order %r",
-                    value_name, clsname, ordered_methods
-                )
-                continue  # pragma: no cover
+                if name not in allowed_next_methods:
+                    value_name = value.__qualname__
+                    logging.warning(
+                        "Method %s not defined at the correct location."
+                        " Methods in class %s must be defined in the following"
+                        " order %r",
+                        value_name, clsname, ordered_methods
+                    )
+                    continue  # pragma: no cover
 
-            _slice = slice(allowed_next_methods.index(name) + 1, None)
-            allowed_next_methods = allowed_next_methods[_slice]
+                _slice = slice(allowed_next_methods.index(name) + 1, None)
+                allowed_next_methods = allowed_next_methods[_slice]
 
-        # Cast to dict is required. We can't pass an OrderedDict here.
-        return super().__new__(cls, clsname, bases, dict(clsdict))
+            # Cast to dict is required. We can't pass an OrderedDict here.
+            return super().__new__(cls, clsname, bases, dict(clsdict))
 
-    @classmethod
-    def __prepare__(cls, clsname, bases):
-        return collections.OrderedDict()
+        @classmethod
+        def __prepare__(cls, clsname, bases):
+            return collections.OrderedDict()
 
-
-class CodingStyleMixin(OrderedMeta, MatchSignaturesMeta, abc.ABCMeta):
-    ordered_methods = ['order', 'check_prerequisite', 'list', 'should_delete',
-                       'delete', 'to_string']
+    class CodingStyleMixin(OrderedMeta, MatchSignaturesMeta, abc.ABCMeta):
+        ordered_methods = ['order', 'check_prerequisite', 'list',
+                           'should_delete', 'delete', 'to_string']
+else:   # pragma: no cover here
+    # OrderedMeta is not supported on Python 2. Class members are unordered in
+    # Python 2 and __prepare__() was introduced in Python 3.
+    class CodingStyleMixin(MatchSignaturesMeta, abc.ABCMeta):
+        pass
 
 
 class BaseServiceResource(object):
@@ -87,11 +94,12 @@ class BaseServiceResource(object):
         self.options = None  # type: Optional[argparse.Namespace]
 
 
-class ServiceResource(BaseServiceResource, metaclass=CodingStyleMixin):
+class ServiceResource(six.with_metaclass(CodingStyleMixin,
+                                         BaseServiceResource)):
     ORDER = None  # type: int
 
     def __init__(self, creds_manager):
-        super().__init__()
+        super(ServiceResource, self).__init__()
         if self.ORDER is None:
             raise ValueError(
                 'Class {}.{} must override the "ORDER" class attribute'.format(

ospurge/resources/base.pyi

@@ -16,6 +16,8 @@ from typing import Dict
 from typing import Iterable
 from typing import Optional
 
+import six
+
 from ospurge.main import CredentialsManager  # noqa: F401
 
 
@@ -48,7 +50,7 @@ class BaseServiceResource(object):
         ...
 
 
-class ServiceResource(BaseServiceResource, metaclass=CodingStyleMixin):
+class ServiceResource(six.with_metaclass(CodingStyleMixin, BaseServiceResource)):
     def __init__(self, creds_manager: 'CredentialsManager') -> None:
         ...
 

ospurge/tests/resources/test_base.py

@@ -11,6 +11,8 @@
 #  under the License.
 import time
 
+import six
+
 from ospurge import exceptions
 from ospurge.resources import base
 from ospurge.tests import mock
@@ -41,7 +43,7 @@ class WrongMethodDefOrder(Exception):
 
 @mock.patch('logging.warning', mock.Mock(side_effect=SignatureMismatch))
 class TestMatchSignaturesMeta(unittest.TestCase):
-    class Test(metaclass=base.MatchSignaturesMeta):
+    class Test(six.with_metaclass(base.MatchSignaturesMeta)):
         def a(self, arg1):
             pass
 
@@ -94,46 +96,48 @@ class TestMatchSignaturesMeta(unittest.TestCase):
                     pass
 
 
-@mock.patch('logging.warning', mock.Mock(side_effect=WrongMethodDefOrder))
-class TestOrderedMeta(unittest.TestCase):
-    class Test(base.OrderedMeta):
-        ordered_methods = ['a', 'b']
+# OrderedMeta requires Python 3
+if six.PY3:
+    @mock.patch('logging.warning', mock.Mock(side_effect=WrongMethodDefOrder))
+    class TestOrderedMeta(unittest.TestCase):
+        class Test(base.OrderedMeta):
+            ordered_methods = ['a', 'b']
 
-    def test_nominal(self):
-        class Foo1(metaclass=self.Test):
-            def a(self):
-                pass
+        def test_nominal(self):
+            class Foo1(six.with_metaclass(self.Test)):
+                def a(self):
+                    pass
 
-        class Foo2(metaclass=self.Test):
-            def b(self):
-                pass
-
-        class Foo3(metaclass=self.Test):
-            def a(self):
-                pass
-
-            def b(self):
-                pass
-
-        class Foo4(metaclass=self.Test):
-            def a(self):
-                pass
-
-            def other(self):
-                pass
-
-            def b(self):
-                pass
-
-    def test_wrong_order(self):
-        with self.assertRaises(WrongMethodDefOrder):
-            class Foo(metaclass=self.Test):
+            class Foo2(six.with_metaclass(self.Test)):
                 def b(self):
                     pass
 
+            class Foo3(six.with_metaclass(self.Test)):
                 def a(self):
                     pass
 
+                def b(self):
+                    pass
+
+            class Foo4(six.with_metaclass(self.Test)):
+                def a(self):
+                    pass
+
+                def other(self):
+                    pass
+
+                def b(self):
+                    pass
+
+        def test_wrong_order(self):
+            with self.assertRaises(WrongMethodDefOrder):
+                class Foo(six.with_metaclass(self.Test)):
+                    def b(self):
+                        pass
+
+                    def a(self):
+                        pass
+
 
 class TestServiceResource(unittest.TestCase):
     def test_init_without_order_attr(self):

requirements.txt

@@ -1,5 +1,6 @@
 os-client-config>=1.22.0  # Apache-2.0
 pbr>=1.8 # Apache-2.0
+six
 shade>=1.13.1
 typing>=3.5.2.2  # PSF