add import_object_ns function

To support bp:virt-driver-cleanup, there is a desire to have shorter
driver strings (i.e. libvirt.LibvirtDriver instead of
nova.virt.libvirt.LibvirtDriver). One way to support this is with
a new import_object variant that takes a namespace to load from.

If the code fails to load the driver in the prefered namespace it
will also try loading the full driver path, before throwing an
exception.

Change-Id: Ib97c92f38685ca89f29890f8015fc413acc744f8

2 files changed, 56 insertions, 0 deletions

diff --git a/openstack/common/importutils.py b/openstack/common/importutils.py
index 7654af5..933b54d 100644
--- a/openstack/common/importutils.py
+++ b/openstack/common/importutils.py
@@ -38,6 +38,19 @@ def import_object(import_str, *args, **kwargs):
     return import_class(import_str)(*args, **kwargs)
 
 
+def import_object_ns(name_space, import_str, *args, **kwargs):
+    """
+    Import a class and return an instance of it, first by trying
+    to find the class in a default namespace, then failing back to
+    a full path if not found in the default namespace.
+    """
+    import_value = "%s.%s" % (name_space, import_str)
+    try:
+        return import_class(import_value)(*args, **kwargs)
+    except ImportError:
+        return import_class(import_str)(*args, **kwargs)
+
+
 def import_module(import_str):
     """Import a module."""
     __import__(import_str)
diff --git a/tests/unit/test_importutils.py b/tests/unit/test_importutils.py
index acdb217..c41f13b 100644
--- a/tests/unit/test_importutils.py
+++ b/tests/unit/test_importutils.py
@@ -58,6 +58,49 @@ class ImportUtilsTest(unittest.TestCase):
                                         first_arg=False)
         self.assertTrue(obj.__class__.__name__, 'FakeDriver2')
 
+    # namespace tests
+    def test_import_object_ns_optional_arg_not_present(self):
+        obj = importutils.import_object_ns('tests.unit', 'fake.FakeDriver')
+        self.assertTrue(obj.__class__.__name__, 'FakeDriver')
+
+    def test_import_object_ns_optional_arg_present(self):
+        obj = importutils.import_object_ns('tests.unit', 'fake.FakeDriver',
+                                        first_arg=False)
+        self.assertTrue(obj.__class__.__name__, 'FakeDriver')
+
+    def test_import_object_ns_required_arg_not_present(self):
+        # arg 1 isn't optional here
+        self.assertRaises(TypeError, importutils.import_object_ns,
+                          'tests.unit', 'fake.FakeDriver2')
+
+    def test_import_object_ns_required_arg_present(self):
+        obj = importutils.import_object_ns('tests.unit', 'fake.FakeDriver2',
+                                        first_arg=False)
+        self.assertTrue(obj.__class__.__name__, 'FakeDriver2')
+
+    # namespace tests
+    def test_import_object_ns_full_optional_arg_not_present(self):
+        obj = importutils.import_object_ns('tests.unit2',
+                                           'tests.unit.fake.FakeDriver')
+        self.assertTrue(obj.__class__.__name__, 'FakeDriver')
+
+    def test_import_object_ns_full_optional_arg_present(self):
+        obj = importutils.import_object_ns('tests.unit2',
+                                           'tests.unit.fake.FakeDriver',
+                                           first_arg=False)
+        self.assertTrue(obj.__class__.__name__, 'FakeDriver')
+
+    def test_import_object_ns_full_required_arg_not_present(self):
+        # arg 1 isn't optional here
+        self.assertRaises(TypeError, importutils.import_object_ns,
+                          'tests.unit2', 'tests.unit.fake.FakeDriver2')
+
+    def test_import_object_ns_full_required_arg_present(self):
+        obj = importutils.import_object_ns('tests.unit2',
+                                           'tests.unit.fake.FakeDriver2',
+                                           first_arg=False)
+        self.assertTrue(obj.__class__.__name__, 'FakeDriver2')
+
     def test_import_object(self):
         dt = importutils.import_object('datetime.time')
         self.assertTrue(isinstance(dt, sys.modules['datetime'].time))