Remove plugin functionality from io.py. Implement setting default plugins and querying the plugins available.

scikits/image/io/__init__.py

@@ -4,6 +4,7 @@ import pil_plugin
 import matplotlib_plugin
 
 from plugin import register as register_plugin
+
 from sift import *
 from collection import *
 

scikits/image/io/io.py

@@ -1,40 +1,6 @@
 __all__ = ['imread', 'imsave', 'imshow']
 
-from scikits.image.io.plugin import plugin_store
-
-def _call_plugin(kind, *args, **kwargs):
-    """Find the appropriate plugin of 'kind' and execute it.
-
-    Parameters
-    ----------
-    kind : {'imshow', 'imsave', 'imread'}
-        Function to look up.
-    plugin : str, optional
-        Plugin to load.  Defaults to None, in which case the first
-        matching plugin is used.
-    *args, **kwargs : arguments and keyword arguments
-        Passed to the plugin function.
-
-    """
-    if not kind in plugin_store:
-        raise ValueError('Invalid function (%s) requested.' % kind)
-
-    plugin_funcs = plugin_store[kind]
-    if len(plugin_funcs) == 0:
-        raise RuntimeError('No suitable plugin registered for %s' % kind)
-
-    plugin = kwargs.pop('plugin', None)
-    if plugin is None:
-        _, func = plugin_funcs[0]
-    else:
-        try:
-            func = [f for (p,f) in plugin_funcs if p == plugin][0]
-        except IndexError:
-            raise RuntimeError('Could not find the plugin "%s" for %s.' % \
-                               (plugin, kind))
-
-    return func(*args, **kwargs)
-
+from scikits.image.io import plugin as _plugin
 
 def imread(fname, as_grey=False, dtype=None, plugin=None, flatten=None,
            **plugin_args):
@@ -78,7 +44,7 @@ def imread(fname, as_grey=False, dtype=None, plugin=None, flatten=None,
     if flatten is not None:
         as_grey = flatten
 
-    return _call_plugin('read', fname, as_grey=as_grey, dtype=dtype,
+    return _plugin.call('read', fname, as_grey=as_grey, dtype=dtype,
                         plugin=plugin, **plugin_args)
 
 def imsave(fname, arr, plugin=None, **plugin_args):
@@ -101,7 +67,7 @@ def imsave(fname, arr, plugin=None, **plugin_args):
         Passed to the given plugin.
 
     """
-    return _call_plugin('save', fname, arr, plugin=plugin, **plugin_args)
+    return _plugin.call('save', fname, arr, plugin=plugin, **plugin_args)
 
 def imshow(arr, plugin=None, **plugin_args):
     """Display an image.
@@ -121,4 +87,4 @@ def imshow(arr, plugin=None, **plugin_args):
         Passed to the given plugin.
 
     """
-    return _call_plugin('show', arr, plugin=plugin, **plugin_args)
+    return _plugin.call('show', arr, plugin=plugin, **plugin_args)

scikits/image/io/plugin.py

@@ -2,6 +2,10 @@
 
 """
 
+__all__ = ['register', 'use']
+
+import warnings
+
 plugin_store = {'read': [],
                 'save': [],
                 'show': []}
@@ -35,3 +39,105 @@ def register(name, **kwds):
             raise ValueError('Can only register functions as plugins.')
 
         plugin_store[kind].append((name, func))
+
+
+def call(kind, *args, **kwargs):
+    """Find the appropriate plugin of 'kind' and execute it.
+
+    Parameters
+    ----------
+    kind : {'show', 'save', 'read'}
+        Function to look up.
+    plugin : str, optional
+        Plugin to load.  Defaults to None, in which case the first
+        matching plugin is used.
+    *args, **kwargs : arguments and keyword arguments
+        Passed to the plugin function.
+
+    """
+    if not kind in plugin_store:
+        raise ValueError('Invalid function (%s) requested.' % kind)
+
+    plugin_funcs = plugin_store[kind]
+    if len(plugin_funcs) == 0:
+        raise RuntimeError('No suitable plugin registered for %s' % kind)
+
+    plugin = kwargs.pop('plugin', None)
+    if plugin is None:
+        _, func = plugin_funcs[0]
+    else:
+        try:
+            func = [f for (p,f) in plugin_funcs if p == plugin][0]
+        except IndexError:
+            raise RuntimeError('Could not find the plugin "%s" for %s.' % \
+                               (plugin, kind))
+
+    return func(*args, **kwargs)
+
+def use(name, kind=None):
+    """Set the default plugin for a specified operation.
+
+    Parameters
+    ----------
+    name : str
+        Name of plugin.
+    kind : {'save', 'read', 'show'}, optional
+        Set the plugin for this function.  By default,
+        the plugin is set for all functions.
+
+    Examples
+    --------
+
+    Use Python Imaging Library to read images:
+
+    >>> from scikits.image.io import plugin
+    >>> plugin.use('PIL', 'read')
+
+    """
+    if kind is None:
+        kind = plugin_store.keys()
+    else:
+        kind = [kind]
+
+    for k in kind:
+        if not k in plugin_store:
+            raise RuntimeError("Could not find plugin for '%s'" % k)
+
+        funcs = plugin_store[k]
+
+        # Shuffle the plugins so that the requested plugin stands first
+        # in line
+        funcs = [(n, f) for (n, f) in funcs if n == name] + \
+                [(n, f) for (n, f) in funcs if n != name]
+
+        n, f = funcs[0]
+        if not n == name:
+            warnings.warn(RuntimeWarning('Could not set plugin "%s" for'
+                                         ' function "%s".' % (name, k)))
+
+        plugin_store[k] = funcs
+
+def available(kind=None):
+    """List available plugins.
+
+    Parameters
+    ----------
+    kind : {'show', 'save', 'read'}, optional
+        Display the plugin list for the given function type.  If not specified,
+        return a dictionary with the plugins for all functions.
+
+    """
+    if kind is None:
+        kind = plugin_store.keys()
+    else:
+        kind = [kind]
+
+    d = {}
+    for k in kind:
+        if not k in plugin_store:
+            raise ValueError('No function "%s" exists in the plugin registry.'
+                             % kind)
+
+        d[k] = [name for (name, func) in plugin_store[k]]
+
+    return d

scikits/image/io/tests/test_plugin.py

@@ -18,9 +18,13 @@ def show(arr, plugin_arg=None):
     assert arr == [1, 2, 3]
     assert plugin_arg == (1, 2)
 
+def show_other(arr):
+    return "other"
+
 def setup_module(self):
     self.backup_plugin_store = deepcopy(plugin.plugin_store)
     plugin.register('test', read=read, save=save, show=show)
+    plugin.register('other', show=show_other)
 
 def teardown_module(self):
     plugin.plugin_store = self.backup_plugin_store
@@ -35,5 +39,14 @@ class TestPlugin:
     def test_show(self):
         io.imshow([1, 2, 3], plugin_arg=(1, 2), plugin='test')
 
+    def test_use(self):
+        plugin.use('other', 'show')
+        assert io.imshow(None) == 'other'
+
+    def test_available(self):
+        plugin.use('other', 'show')
+        d = plugin.available('show')
+        assert d['show'][0] == 'other'
+
 if __name__ == "__main__":
     run_module_suite()