BUG: Fix selective plugin loading. Provide function to inspect current plugin configuration.

skimage/io/__init__.py

@@ -7,6 +7,7 @@ The following plug-ins are available:
 from ._plugins import use as use_plugin
 from ._plugins import available as plugins
 from ._plugins import info as plugin_info
+from ._plugins import configuration as plugin_order
 available_plugins = plugins()
 
 for preferred_plugin in ['pil', 'matplotlib', 'qt', 'null']:

skimage/io/_plugins/plugin.py

@@ -2,7 +2,7 @@
 
 """
 
-__all__ = ['use', 'available', 'call', 'info']
+__all__ = ['use', 'available', 'call', 'info', 'configuration']
 
 import warnings
 from ConfigParser import ConfigParser
@@ -145,6 +145,12 @@ def available(loaded=False):
         If True, show only those plugins currently loaded.  By default,
         all plugins are shown.
 
+    Returns
+    -------
+    p : dict
+        Dictionary with plugin names as keys and exposed functions as
+        values.
+
     """
     active_plugins = set()
     for plugin_func in plugin_store.itervalues():
@@ -187,8 +193,8 @@ def _load(plugin):
         else:
             store = plugin_store[p]
             func = getattr(plugin_module, p)
-            if not func in store:
-                store.insert(0, (plugin, func))
+            if not (plugin, func) in store:
+                store.append((plugin, func))
 
 def info(plugin):
     """Return plugin meta-data.
@@ -209,3 +215,17 @@ def info(plugin):
     except KeyError:
         raise ValueError('No information on plugin "%s"' % plugin)
 
+def configuration():
+    """Return the currently preferred plugin order.
+
+    Returns
+    -------
+    p : dict
+        Dictionary of preferred plugin order, with function name as key and
+        plugins (in order of preference) as value.
+
+    """
+    p = {}
+    for func in plugin_store:
+        p[func] = [plugin_name for (plugin_name, f) in plugin_store[func]]
+    return p

skimage/io/tests/test_plugin.py

@@ -53,14 +53,34 @@ class TestPlugin:
     def test_use_priority(self):
         plugin.use(priority_plugin)
         plug, func = plugin.plugin_store['imread'][0]
-        print(plugin.plugin_store)
         assert_equal(plug, priority_plugin)
 
         plugin.use('test')
         plug, func = plugin.plugin_store['imread'][0]
-        print(plugin.plugin_store)
         assert_equal(plug, 'test')
 
+    @skipif(not PIL_available)
+    def test_use_priority_with_func(self):
+        plugin.use('pil')
+        plug, func = plugin.plugin_store['imread'][0]
+        assert_equal(plug, 'pil')
+
+        plugin.use('test', 'imread')
+        plug, func = plugin.plugin_store['imread'][0]
+        assert_equal(plug, 'test')
+
+        plug, func = plugin.plugin_store['imsave'][0]
+        assert_equal(plug, 'pil')
+
+        plugin.use('test')
+        plug, func = plugin.plugin_store['imsave'][0]
+        assert_equal(plug, 'test')
+
+    def test_plugin_order(self):
+        p = io.plugin_order()
+        assert 'imread' in p
+        assert 'test' in p['imread']
+
     def test_available(self):
         assert 'qt' in io.plugins()
         assert 'test' in io.plugins(loaded=True)