Implement importutils.try_import.

Adds a new (simple) importutils.try_import function which
can return a module name or a default (by default this is None).

This should help clean up some of our

try:
    import foo
except...

blocks in modules.

This commit also drops the dependency on python-extras which is
no longer needed.

Fixes LP Bug #1099501.

Change-Id: I8591f79983bdad67a50d1aaae6dce8428dfce084

openstack/common/importutils.py

@@ -57,3 +57,11 @@ def import_module(import_str):
     """Import a module."""
     __import__(import_str)
     return sys.modules[import_str]
+
+
+def try_import(import_str, default=None):
+    """Try to import a module and if it fails return default."""
+    try:
+        return import_module(import_str)
+    except ImportError:
+        return default

openstack/common/service.py

@@ -27,17 +27,17 @@ import sys
 import time
 
 import eventlet
-import extras
 import logging as std_logging
 
 from openstack.common import cfg
 from openstack.common import eventlet_backdoor
 from openstack.common.gettextutils import _
+from openstack.common import importutils
 from openstack.common import log as logging
 from openstack.common import threadgroup
 
 
-rpc = extras.try_import('openstack.common.rpc')
+rpc = importutils.try_import('openstack.common.rpc')
 CONF = cfg.CONF
 LOG = logging.getLogger(__name__)
 

tests/unit/test_importutils.py

@@ -109,3 +109,11 @@ class ImportUtilsTest(unittest.TestCase):
         dt = importutils.import_object('datetime.datetime', 2012, 4, 5)
         self.assertTrue(isinstance(dt, sys.modules['datetime'].datetime))
         self.assertEqual(dt, datetime.datetime(2012, 4, 5))
+
+    def test_try_import(self):
+        dt = importutils.try_import('datetime')
+        self.assertEqual(sys.modules['datetime'], dt)
+
+    def test_try_import_returns_default(self):
+        foo = importutils.try_import('foo.bar')
+        self.assertEqual(None, foo)

tools/pip-requires

@@ -1,7 +1,6 @@
 PasteDeploy==1.5.0
 WebOb==1.2.3
 eventlet
-extras
 greenlet>=0.3.1
 lxml
 routes==1.12.3