Add code to dynamically import a class.

.gitignore

@@ -4,3 +4,4 @@
 dist
 build
 .cache
+*.swp

libra/worker/drivers/base.py

@@ -12,6 +12,12 @@
 # License for the specific language governing permissions and limitations
 
 
+# Mapping of --driver options to a class
+known_drivers = {
+    'haproxy': 'libra.worker.drivers.haproxy.driver.HAProxyDriver'
+}
+
+
 class LoadBalancerDriver(object):
     """
     Load balancer device driver base class.

libra/worker/utils.py

@@ -0,0 +1,29 @@
+# Copyright 2012 Hewlett-Packard Development Company, L.P.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+import importlib
+import sys
+import traceback
+
+
+def import_class(import_str):
+    """ Returns a class from a string including module and class """
+    mod_str, _sep, class_str = import_str.rpartition('.')
+    try:
+        mod = importlib.import_module(mod_str, 'libra.worker.drivers')
+        return getattr(mod, class_str)
+    except (ValueError, AttributeError):
+        raise ImportError('Class %s cannot be found (%s)' %
+                          (class_str,
+                           traceback.format_exception(*sys.exc_info())))

libra/worker/worker.py

@@ -22,6 +22,8 @@ from time import sleep
 from libra.common.json_gearman import JSONGearmanWorker
 from libra.common.faults import BadRequest
 from libra.common.options import Options, setup_logging
+from libra.worker.drivers.base import known_drivers
+from libra.worker.utils import import_class
 
 
 def lbaas_task(worker, job):
@@ -81,6 +83,7 @@ def lbaas_task(worker, job):
 
 
 class CustomJSONGearmanWorker(JSONGearmanWorker):
+    """ Custom class we will use to pass arguments to the Gearman task. """
     logger = None
     driver = None
 
@@ -133,14 +136,22 @@ def main():
         default=60, help='seconds to sleep between job server reconnects'
     )
     options.parser.add_argument(
-        '--driver', dest='driver', default='haproxy.driver.HAProxyDriver',
-        help='Class name of device driver to use'
+        '--driver', dest='driver',
+        choices=known_drivers.keys(), default='haproxy',
+        help='Type of device to use'
     )
     args = options.run()
 
     logger = setup_logging('libra_worker', args)
-    from libra.worker.drivers.haproxy.driver import HAProxyDriver
-    driver = HAProxyDriver()
+
+    # Import the device driver we are going to use. This will be sent
+    # along to the Gearman task that will use it to communicate with
+    # the device.
+
+    logger.debug("Using driver %s=%s" % (args.driver,
+                                         known_drivers[args.driver]))
+    driver_class = import_class(known_drivers[args.driver])
+    driver = driver_class()
 
     server = Server(['localhost:4730'], args.reconnect_sleep)
     server.logger = logger