From f0da043cb82ad73b4f0c057549f97045b35d2710 Mon Sep 17 00:00:00 2001
From: Doug Hellmann <doug.hellmann@dreamhost.com>
Date: Tue, 19 Jun 2012 16:14:31 -0400
Subject: [PATCH] add DriverManager

---
 stevedore/__init__.py          |  2 ++
 stevedore/driver.py            | 24 ++++++++++++++++++++++++
 stevedore/tests/test_driver.py | 17 +++++++++++++++++
 3 files changed, 43 insertions(+)
 create mode 100644 stevedore/driver.py
 create mode 100644 stevedore/tests/test_driver.py

diff --git a/stevedore/__init__.py b/stevedore/__init__.py
index 958ab7e..9b19761 100644
--- a/stevedore/__init__.py
+++ b/stevedore/__init__.py
@@ -1,3 +1,5 @@
 from .extension import ExtensionManager
 from .enabled import EnabledExtensionManager
 from .named import NamedExtensionManager
+from .hook import HookManager
+from .driver import DriverManager
diff --git a/stevedore/driver.py b/stevedore/driver.py
new file mode 100644
index 0000000..9c0effc
--- /dev/null
+++ b/stevedore/driver.py
@@ -0,0 +1,24 @@
+from .hook import HookManager
+
+
+class DriverManager(HookManager):
+    """Load a single plugin with a given name from the namespace.
+    """
+
+    def __init__(self, namespace, name,
+                 invoke_on_load=False, invoke_args=(), invoke_kwds={}):
+        super(HookManager, self).__init__(
+            namespace,
+            [name],
+            invoke_on_load=invoke_on_load,
+            invoke_args=invoke_args,
+            invoke_kwds=invoke_kwds,
+            )
+        if not self.extensions:
+            raise RuntimeError('No %r driver found' % namespace)
+        if len(self.extensions) > 1:
+            raise RuntimeError('Multiple %r drivers found: %s' %
+                               (namespace,
+                                ','.join('%s:%s' % (e.module_name, e.attrs[0])
+                                         for e in self.extensions))
+                               )
diff --git a/stevedore/tests/test_driver.py b/stevedore/tests/test_driver.py
new file mode 100644
index 0000000..984eaac
--- /dev/null
+++ b/stevedore/tests/test_driver.py
@@ -0,0 +1,17 @@
+"""Tests for stevedore.extension
+"""
+
+from stevedore import driver
+
+
+def test_detect_plugins():
+    em = driver.DriverManager('stevedore.test.extension', 't1')
+    names = sorted(em.names())
+    assert names == ['t1']
+
+
+def test_no_drivers():
+    try:
+        driver.DriverManager('stevedore.test.extension.none', 't1')
+    except RuntimeError as err:
+        assert "No 'stevedore.test.extension.none' driver found" == str(err)