From 20a5df58fd16040a2ab997f1732548bbcce24a27 Mon Sep 17 00:00:00 2001
From: Thomas Robitaille <thomas.robitaille@gmail.com>
Date: Tue, 17 Mar 2015 23:09:59 +0100
Subject: [PATCH 1/7] Allow plugins to be registered with registries then
 loaded when needed

---
 glue/__init__.py            |  5 ++++-
 glue/config.py              | 14 ++++++++++++++
 glue/plugins/__init__.py    | 14 +++++++++-----
 glue/qt/glue_application.py |  4 ----
 4 files changed, 27 insertions(+), 10 deletions(-)

diff --git a/glue/__init__.py b/glue/__init__.py
index 28d6d8fd2..6581de8b0 100644
--- a/glue/__init__.py
+++ b/glue/__init__.py
@@ -118,13 +118,16 @@ def make_selector_func(roi):
     from .qt.custom_viewer import CustomViewer
     return CustomViewer.create_new_subclass(name, **kwargs)
 
+# Register default plugins (but don't load them)
+from .plugins import register_plugins
+register_plugins()
+
 # Load user's configuration file
 from .config import load_configuration
 env = load_configuration()
 
 from .qglue import qglue
 
-
 from .version import __version__
 
 def test(no_optional_skip=False):
diff --git a/glue/config.py b/glue/config.py
index eb7769f76..7b56a5174 100644
--- a/glue/config.py
+++ b/glue/config.py
@@ -35,6 +35,7 @@ class Registry(object):
 
     def __init__(self):
         self._members = []
+        self._plugins = []
         self._loaded = False
 
     @property
@@ -42,6 +43,7 @@ def members(self):
         """ A list of the members in the registry.
         The return value is a list. The contents of the list
         are specified in each subclass"""
+        self._load_plugins()
         if not self._loaded:
             self._members = self.default_members() + self._members
             self._loaded = True
@@ -57,6 +59,18 @@ def add(self, value):
         """ Add a new item to the registry """
         self._members.append(value)
 
+    def add_plugin(self, value):
+        """
+        Add a plugin that will populate this registry
+        """
+        self._plugins.append(value)
+
+    def _load_plugins(self):
+        from .plugins import load_plugin
+        while self._plugins:
+            plugin = self._plugins.pop()
+            load_plugin(plugin)
+
     def __iter__(self):
         return iter(self.members)
 
diff --git a/glue/plugins/__init__.py b/glue/plugins/__init__.py
index 3ef21f8b5..b36cebbd9 100644
--- a/glue/plugins/__init__.py
+++ b/glue/plugins/__init__.py
@@ -3,10 +3,14 @@
 from . import ginga_viewer
 
 
-def load_all_plugins():
+def register_plugins():
+    from ..config import qt_client
+    qt_client.register_plugin('glue.plugins.ginga_viewer')
+    
+
+def load_plugin(plugin):
     """
-    Load built-in plugins
+    Load plugin referred to by name 'plugin'
     """
-
-    from .ginga_viewer import load_ginga_viewer_plugin
-    load_ginga_viewer_plugin()
+    # TODO: load plugin here
+    print("LOADING", plugin)
\ No newline at end of file
diff --git a/glue/qt/glue_application.py b/glue/qt/glue_application.py
index 8caa70be4..5cc57761a 100644
--- a/glue/qt/glue_application.py
+++ b/glue/qt/glue_application.py
@@ -179,10 +179,6 @@ def __init__(self, data_collection=None, session=None):
         Application.__init__(self, data_collection=data_collection,
                              session=session)
 
-        # Load all plugins
-        from ..plugins import load_all_plugins
-        load_all_plugins()
-
         self.app = get_qapp()
 
         self.setWindowIcon(self.app.windowIcon())

From 1e8f02365384a9ec0b00b67e8fc282a8a5aaa749 Mon Sep 17 00:00:00 2001
From: Thomas Robitaille <thomas.robitaille@gmail.com>
Date: Tue, 17 Mar 2015 23:17:20 +0100
Subject: [PATCH 2/7] More tidying up

---
 glue/plugins/__init__.py              | 11 +++++++----
 glue/plugins/export_d3po.py           |  7 +++++--
 glue/plugins/export_plotly.py         | 11 +++++++----
 glue/plugins/ginga_viewer/__init__.py |  2 +-
 4 files changed, 20 insertions(+), 11 deletions(-)

diff --git a/glue/plugins/__init__.py b/glue/plugins/__init__.py
index b36cebbd9..4f4ae6e70 100644
--- a/glue/plugins/__init__.py
+++ b/glue/plugins/__init__.py
@@ -4,13 +4,16 @@
 
 
 def register_plugins():
-    from ..config import qt_client
-    qt_client.register_plugin('glue.plugins.ginga_viewer')
+    from ..config import qt_client, exporters
+    qt_client.add_plugin('glue.plugins.ginga_viewer')
+    exporters.add_plugin('glue.plugins.export_d3po')
+    exporters.add_plugin('glue.plugins.export_plotly')
     
 
 def load_plugin(plugin):
     """
     Load plugin referred to by name 'plugin'
     """
-    # TODO: load plugin here
-    print("LOADING", plugin)
\ No newline at end of file
+    import importlib
+    module = importlib.import_module(plugin)
+    module.load_plugin()
diff --git a/glue/plugins/export_d3po.py b/glue/plugins/export_d3po.py
index 9ffc4cd1a..82f74deca 100644
--- a/glue/plugins/export_d3po.py
+++ b/glue/plugins/export_d3po.py
@@ -3,7 +3,6 @@
 import json
 import os
 
-from ..config import exporters
 from ..qt.widgets import ScatterWidget, HistogramWidget
 from ..core import Subset
 
@@ -247,7 +246,11 @@ def launch(path):
     webbrowser.open('http://0.0.0.0:%i' % PORT)
 
 
-exporters.add('D3PO', save_d3po, can_save_d3po, outmode='directory')
+def load_plugin():
+    from ..logger import logger
+    from ..config import exporters
+    exporters.add('D3PO', save_d3po, can_save_d3po, outmode='directory')
+    logger.info("Loaded d3po exporter plugin")
 
 
 HTML = """
diff --git a/glue/plugins/export_plotly.py b/glue/plugins/export_plotly.py
index 78f3d129d..a15592c5b 100644
--- a/glue/plugins/export_plotly.py
+++ b/glue/plugins/export_plotly.py
@@ -6,7 +6,6 @@
 except ImportError:
     plotly = None
 
-from ..config import exporters, settings
 from ..qt.widgets import ScatterWidget, HistogramWidget
 from ..core.data import CategoricalComponent
 from ..core.layout import Rectangle, snap_to_grid
@@ -305,6 +304,10 @@ def save_plotly(application, label):
     plotly.sign_in(user, apikey)
     plotly.plot(*args, **kwargs)
 
-exporters.add('Plotly', save_plotly, can_save_plotly, outmode='label')
-settings.add('PLOTLY_USER', 'Glue')
-settings.add('PLOTLY_APIKEY', 't24aweai14')
+def load_plugin():
+    from ..logger import logger
+    from ..config import exporters, settings
+    exporters.add('Plotly', save_plotly, can_save_plotly, outmode='label')
+    settings.add('PLOTLY_USER', 'Glue')
+    settings.add('PLOTLY_APIKEY', 't24aweai14')
+    logger.info("Loaded plotly exporter plugin")
diff --git a/glue/plugins/ginga_viewer/__init__.py b/glue/plugins/ginga_viewer/__init__.py
index cf197fa21..a84a67fe0 100644
--- a/glue/plugins/ginga_viewer/__init__.py
+++ b/glue/plugins/ginga_viewer/__init__.py
@@ -1,4 +1,4 @@
-def load_ginga_viewer_plugin():
+def load_plugin():
     from ...logger import logger
     try:
         from .qt_widget import GingaWidget

From 1254236c6aeb570a47c8ce713efc832f6e640f34 Mon Sep 17 00:00:00 2001
From: Thomas Robitaille <thomas.robitaille@gmail.com>
Date: Wed, 18 Mar 2015 21:36:21 +0100
Subject: [PATCH 3/7] Rename add_plugin to lazy_add, and load_plugin to setup

---
 glue/config.py                        |  8 +++++---
 glue/plugins/__init__.py              | 11 +++++++----
 glue/plugins/export_d3po.py           |  2 +-
 glue/plugins/export_plotly.py         |  2 +-
 glue/plugins/ginga_viewer/__init__.py |  2 +-
 5 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/glue/config.py b/glue/config.py
index 7b56a5174..e5a56f16d 100644
--- a/glue/config.py
+++ b/glue/config.py
@@ -56,12 +56,14 @@ def default_members(self):
         return []
 
     def add(self, value):
-        """ Add a new item to the registry """
+        """
+        Add a new item to the registry.
+        """
         self._members.append(value)
 
-    def add_plugin(self, value):
+    def lazy_add(self, value):
         """
-        Add a plugin that will populate this registry
+        Add a reference to a plugin which will be loaded when needed.
         """
         self._plugins.append(value)
 
diff --git a/glue/plugins/__init__.py b/glue/plugins/__init__.py
index 4f4ae6e70..a24c01d80 100644
--- a/glue/plugins/__init__.py
+++ b/glue/plugins/__init__.py
@@ -5,9 +5,9 @@
 
 def register_plugins():
     from ..config import qt_client, exporters
-    qt_client.add_plugin('glue.plugins.ginga_viewer')
-    exporters.add_plugin('glue.plugins.export_d3po')
-    exporters.add_plugin('glue.plugins.export_plotly')
+    qt_client.lazy_add('glue.plugins.ginga_viewer')
+    exporters.lazy_add('glue.plugins.export_d3po')
+    exporters.lazy_add('glue.plugins.export_plotly')
     
 
 def load_plugin(plugin):
@@ -16,4 +16,7 @@ def load_plugin(plugin):
     """
     import importlib
     module = importlib.import_module(plugin)
-    module.load_plugin()
+    if hasattr(module, 'setup'):
+        module.setup()
+    else:
+        raise AttributeError("Plugin {0} should define 'setup' function".format(plugin))
diff --git a/glue/plugins/export_d3po.py b/glue/plugins/export_d3po.py
index 82f74deca..8157848bf 100644
--- a/glue/plugins/export_d3po.py
+++ b/glue/plugins/export_d3po.py
@@ -246,7 +246,7 @@ def launch(path):
     webbrowser.open('http://0.0.0.0:%i' % PORT)
 
 
-def load_plugin():
+def setup():
     from ..logger import logger
     from ..config import exporters
     exporters.add('D3PO', save_d3po, can_save_d3po, outmode='directory')
diff --git a/glue/plugins/export_plotly.py b/glue/plugins/export_plotly.py
index a15592c5b..2ed2a150b 100644
--- a/glue/plugins/export_plotly.py
+++ b/glue/plugins/export_plotly.py
@@ -304,7 +304,7 @@ def save_plotly(application, label):
     plotly.sign_in(user, apikey)
     plotly.plot(*args, **kwargs)
 
-def load_plugin():
+def setup():
     from ..logger import logger
     from ..config import exporters, settings
     exporters.add('Plotly', save_plotly, can_save_plotly, outmode='label')
diff --git a/glue/plugins/ginga_viewer/__init__.py b/glue/plugins/ginga_viewer/__init__.py
index a84a67fe0..a602abe5b 100644
--- a/glue/plugins/ginga_viewer/__init__.py
+++ b/glue/plugins/ginga_viewer/__init__.py
@@ -1,4 +1,4 @@
-def load_plugin():
+def setup():
     from ...logger import logger
     try:
         from .qt_widget import GingaWidget

From 5dd86f7dd4695145ba0af889be364126168cb71a Mon Sep 17 00:00:00 2001
From: Thomas Robitaille <thomas.robitaille@gmail.com>
Date: Wed, 18 Mar 2015 23:10:29 +0100
Subject: [PATCH 4/7] Added documentation about plugins

---
 doc/gui_guide/configuration.rst    |   1 -
 doc/python_guide/customization.rst | 150 +++++++++++++++++++++++------
 glue/config.py                     |   7 +-
 3 files changed, 126 insertions(+), 32 deletions(-)

diff --git a/doc/gui_guide/configuration.rst b/doc/gui_guide/configuration.rst
index c03befb43..028716be6 100644
--- a/doc/gui_guide/configuration.rst
+++ b/doc/gui_guide/configuration.rst
@@ -24,7 +24,6 @@ To obtain a fresh ``config.py`` file to edit, run the command line program::
 
 Which will create a new file at ``~/.glue/config.py``
 
-
 Example Usage: Custom Link Functions
 ------------------------------------
 
diff --git a/doc/python_guide/customization.rst b/doc/python_guide/customization.rst
index 34467792a..7b8fc75df 100644
--- a/doc/python_guide/customization.rst
+++ b/doc/python_guide/customization.rst
@@ -2,26 +2,48 @@
 
 Customizing Glue
 ================
-There are a few ways to customize the Glue UI
-with configuration files and plugins.
 
+There are a few ways to customize the Glue UI with configuration files and
+plugins.
 
 Configuration Files
 -------------------
 
-Each time Glue starts, it looks for and executes a configuration file. This is a normal python script into which users can define or import new functions to link data, plug in their own visualization modules, set up logging, etc.
+Each time Glue starts, it looks for and executes a configuration file. This
+is a normal python script into which users can define or import new functions
+to link data, plug in their own visualization modules, set up logging, etc.
 
-The glue configuration file is called ``config.py``. Glue looks for this file in the following locations, in order:
+The glue configuration file is called ``config.py``. Glue looks for this file
+in the following locations, in order:
 
  * The current working directory
  * The path specified in the ``GLUERC`` environment variable, if present
  * The path ``.glue/config.py`` within the user's home directory
 
+Registries
+----------
+
+Glue is written so as to allow users to easily register new plug-in data
+viewers, tools, exporters, and more. Registering such plug-ins can be done
+via *registries* located in the ``glue.config`` sub-package. Registries
+include for example ``link_function``, ``data_factory``, ``colormaps``, and
+so on. As demonstrated below, some registries can be used as decorators (see
+e.g. `Adding Custom Link Functions`_) and for others you can add items using
+the ``add`` method (see e.g. `Custom Colormaps`_).
+
+In the following sections, we show a few examples of registering new
+functionality, and a full list of available registries is given in `Complete
+list of registries`_.
+
 Adding Custom Link Functions
 ----------------------------
 .. _custom_links:
 
-From the :ref:`Link Data Dialog <getting_started_link>`, you inform Glue how to convert between quantities among different data sets. You do this by selecting a translation function, and specifying which data attributes should be treated as inputs and outputs. You can use the configuration file to specify custom translation functions. Here's how:
+From the :ref:`Link Data Dialog <getting_started_link>`, you inform Glue how
+to convert between quantities among different data sets. You do this by
+selecting a translation function, and specifying which data attributes should
+be treated as inputs and outputs. You can use the configuration file to
+specify custom translation functions. Here's how:
 
 .. literalinclude:: scripts/config_link_example.py
 
@@ -30,14 +52,15 @@ Some remarks about this code:
  #. We provide a short summary of the function in the ``info`` keyword, and a list of ``output_labels``. Usually, only one quantity is returned, so ``output_labels`` has one element.
  #. Glue will always pass numpy arrays as inputs to a link function, and expects a numpy array (or a tuple of numpy arrays) as output
 
-With this code in your configuration file, the ``deg_to_rad`` function is available in the ``Link Data`` dialog:
+With this code in your configuration file, the ``deg_to_rad`` function is
+available in the ``Link Data`` dialog:
 
 .. figure:: images/custom_link.png
    :align: center
    :width: 200px
 
-This would allow you to link between two datasets with different conventions for specifying angles.
-
+This would allow you to link between two datasets with different conventions
+for specifying angles.
 
 Custom Data Loaders
 -------------------
@@ -46,10 +69,10 @@ Custom Data Loaders
 Glue lets you create custom data loader functions,
 to use from within the GUI.
 
-Here's a quick example: the default image loader in Glue
-reads each color in an RGB image into 3 two-dimensional components.
-Perhaps you want to be able to load these images into a single 3-dimensional
-component called ``cube``. Here's how you could do this::
+Here's a quick example: the default image loader in Glue reads each color in
+an RGB image into 3 two-dimensional components. Perhaps you want to be able
+to load these images into a single 3-dimensional component called ``cube``.
+Here's how you could do this::
 
  from glue.config import data_factory
  from glue.core import Data
@@ -68,12 +91,14 @@ Let's look at this line-by-line:
 * The `is_jpeg` function takes a filename and keywords as input,
   and returns True if a data factory can handle this file
 
-* The ``@data_factory`` decorator is how Glue "finds" this function.
-   Its two arguments are a label, and the `is_jpeg` identifier function
+* The ``@data_factory`` decorator is how Glue "finds" this function. Its two
+  arguments are a label, and the `is_jpeg` identifier function
 
-* The first line in ``read_jpeg`` uses scikit-image to load an image file into a NumPy array.
+* The first line in ``read_jpeg`` uses scikit-image to load an image file
+  into a NumPy array.
 
-* The second line :ref:`constructs a Data object <data_creation>` from this array, and returns the result.
+* The second line :ref:`constructs a Data object <data_creation>` from this
+  array, and returns the result.
 
 If you put this in your ``config.py`` file, you will see a new
 file type when loading data:
@@ -82,15 +107,17 @@ file type when loading data:
      :align: center
      :width: 50%
 
-If you open a file using this file type selection, Glue will pass
-the path of this file to your function, and use the resulting Data
-object.
+If you open a file using this file type selection, Glue will pass the path of
+this file to your function, and use the resulting Data object.
 
-For more examples of custom data loaders, see the `example repository <https://github.com/glue-viz/glue-data-loaders>`_.
+For more examples of custom data loaders, see the `example repository
+<https://github.com/glue-viz/glue-data-loaders>`_.
 
 Custom Colormaps
 ----------------
-You can add additional matplotlib colormaps to Glue's image viewer by adding the following code into ``config.py``::
+
+You can add additional matplotlib colormaps to Glue's image viewer by adding
+the following code into ``config.py``::
 
     from glue.config import colormaps
     from matplotlib.cm import Paired
@@ -98,8 +125,9 @@ You can add additional matplotlib colormaps to Glue's image viewer by adding the
 
 Custom Subset Actions
 ---------------------
-You can add menu items to run custom functions on subsets.
-Use the following pattern in ``config..py``::
+
+You can add menu items to run custom functions on subsets. Use the following
+pattern in ``config..py``::
 
     from glue.config import single_subset_action
 
@@ -108,7 +136,75 @@ Use the following pattern in ``config..py``::
 
     single_subset_action('Menu title', callback)
 
-This menu item is available by right clicking on a subset
-when a single subset is selected in the Data Collection window. Note
-that you must select the subset specific to a particular Data set,
-and not the parent Subset Group.
\ No newline at end of file
+This menu item is available by right clicking on a subset when a single
+subset is selected in the Data Collection window. Note that you must select
+the subset specific to a particular Data set, and not the parent Subset Group.
+
+Complete list of registries
+---------------------------
+
+A few registries have been demonstrated above, and a complete list of main
+registries are listed below. All can be imported from ``glue.config`` - each
+registry is an instance of a class, given in the second column, and which
+provides more information about what the registry is and how it can be used.
+
+========================== =======================================================
+Registry name                  Registry class
+========================== =======================================================
+``qt_client``                :class:`glue.config.QtClientRegistry`
+``tool_registry``            :class:`glue.config.QtToolRegistry`
+``data_factory``             :class:`glue.config.DataFactoryRegistry`
+``link_function``            :class:`glue.config.LinkFunctionRegistry`
+``link_helper``              :class:`glue.config.LinkHelperRegistry`
+``colormaps``                :class:`glue.config.ColormapRegistry`
+``exporters``                :class:`glue.config.ExporterRegistry`
+``settings``                 :class:`glue.config.SettingRegistry`
+``fit_plugin``               :class:`glue.config.ProfileFitterRegistry`
+``single_subset_action``     :class:`glue.config.SingleSubsetLayerActionRegistry`
+========================== =======================================================
+
+Deferring loading of plug-in functionality (advanced)
+-----------------------------------------------------
+
+In some cases, you may want to defer the loading of your plugin until it is
+actually needed. To do this:
+
+* Place the code for your plugin in a file or package that could be imported
+  from the ``config.py`` (but don't import it directly - it just has to be
+  importable)
+
+* Include a function called ``setup`` alongside the plugin, and this function
+  should contain code to actually add your custom tools to the appropriate
+  registries.
+
+* In ``config.py``, you can then add the plugin file or package to a registry
+  by using the ``lazy_add`` method and pass a string giving the name of the
+  package or sub-package containing the plugin.
+
+Imagine that you have created a data viewer ``MyQtViewer``. You could
+directly register it using::
+
+    from glue.config import qt_client
+    qt_client.add(MyQtViewer)
+
+but if you want to defer the loading of the ``MyQtViewer`` class, you can
+place the definition of ``MyQtViewer`` in a file called e.g.
+``my_qt_viewer.py`` that is located in the same directory as your
+``config.py`` file. This file should look something like::
+
+    class MyQtViewer(...):
+        ...
+
+    def setup():
+        from glue.config import qt_client
+        qt_client.add(MyQtViewer)
+
+then in ``config.py``, you can do::
+
+    from glue.config import qt_client
+    qt_client.lazy_add('my_qt_viewer')
+
+With this in place, the ``setup`` in your plugin will only get called if the
+Qt data viewers are needed, but you will avoid unecessarily importing Qt if
+you only want to access ``glue.core``.
+
diff --git a/glue/config.py b/glue/config.py
index e5a56f16d..aee9e9521 100644
--- a/glue/config.py
+++ b/glue/config.py
@@ -11,11 +11,10 @@
 
 __all__ = ['Registry', 'SettingRegistry', 'ExporterRegistry',
            'ColormapRegistry', 'DataFactoryRegistry', 'QtClientRegistry',
-           'LinkFunctionRegistry', 'LinkHelperRegistry',
-           'ProfileFitterRegistry',
+           'LinkFunctionRegistry', 'LinkHelperRegistry', 'QtToolRegistry',
+           'SingleSubsetLayerActionRegistry', 'ProfileFitterRegistry',
            'qt_client', 'data_factory', 'link_function', 'link_helper',
-           'colormaps',
-           'exporters', 'settings', 'fit_plugin', 'auto_refresh']
+           'colormaps', 'exporters', 'settings', 'fit_plugin', 'auto_refresh']
 
 
 class Registry(object):

From ac2b213cc38b970036f53e10a4f171632b3c7aaf Mon Sep 17 00:00:00 2001
From: Thomas Robitaille <thomas.robitaille@gmail.com>
Date: Wed, 18 Mar 2015 23:37:13 +0100
Subject: [PATCH 5/7] =?UTF-8?q?Can=E2=80=99t=20use=20importlib=20as=20long?=
 =?UTF-8?q?=20as=20we=20support=20Python=202.6?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 glue/plugins/__init__.py | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/glue/plugins/__init__.py b/glue/plugins/__init__.py
index a24c01d80..e16f3da34 100644
--- a/glue/plugins/__init__.py
+++ b/glue/plugins/__init__.py
@@ -1,6 +1,4 @@
-from . import export_d3po
-from . import export_plotly
-from . import ginga_viewer
+import sys
 
 
 def register_plugins():
@@ -8,14 +6,17 @@ def register_plugins():
     qt_client.lazy_add('glue.plugins.ginga_viewer')
     exporters.lazy_add('glue.plugins.export_d3po')
     exporters.lazy_add('glue.plugins.export_plotly')
-    
+
 
 def load_plugin(plugin):
     """
     Load plugin referred to by name 'plugin'
     """
-    import importlib
-    module = importlib.import_module(plugin)
+    # When Python 2.6 is no longer supported, we can use:
+    # import importlib
+    # module = importlib.import_module(plugin)
+    __import__(plugin)
+    return sys.modules[plugin]
     if hasattr(module, 'setup'):
         module.setup()
     else:

From 7b53f4b13f4dbd9bb32ab64efade1f68cffbebea Mon Sep 17 00:00:00 2001
From: Thomas Robitaille <thomas.robitaille@gmail.com>
Date: Thu, 19 Mar 2015 00:22:24 +0100
Subject: [PATCH 6/7] Renamed _plugins to _lazy_members

---
 glue/config.py | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/glue/config.py b/glue/config.py
index aee9e9521..3f5fd7fa1 100644
--- a/glue/config.py
+++ b/glue/config.py
@@ -34,7 +34,7 @@ class Registry(object):
 
     def __init__(self):
         self._members = []
-        self._plugins = []
+        self._lazy_members = []
         self._loaded = False
 
     @property
@@ -42,7 +42,7 @@ def members(self):
         """ A list of the members in the registry.
         The return value is a list. The contents of the list
         are specified in each subclass"""
-        self._load_plugins()
+        self._load_lazy_members()
         if not self._loaded:
             self._members = self.default_members() + self._members
             self._loaded = True
@@ -64,12 +64,12 @@ def lazy_add(self, value):
         """
         Add a reference to a plugin which will be loaded when needed.
         """
-        self._plugins.append(value)
+        self._lazy_members.append(value)
 
-    def _load_plugins(self):
+    def _load_lazy_members(self):
         from .plugins import load_plugin
-        while self._plugins:
-            plugin = self._plugins.pop()
+        while self._lazy_members:
+            plugin = self._lazy_members.pop()
             load_plugin(plugin)
 
     def __iter__(self):

From 238241d718eece62b96657f5ad9d5aba821938aa Mon Sep 17 00:00:00 2001
From: Thomas Robitaille <thomas.robitaille@gmail.com>
Date: Thu, 19 Mar 2015 00:34:08 +0100
Subject: [PATCH 7/7] Make PV slicer and spectrum tool use new plugin lazy
 loading

---
 glue/config.py                      | 2 ++
 glue/plugins/__init__.py            | 4 +++-
 glue/plugins/tools/pv_slicer.py     | 8 ++++++++
 glue/plugins/tools/spectrum_tool.py | 8 ++++++++
 glue/qt/widgets/image_widget.py     | 4 +---
 5 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/glue/config.py b/glue/config.py
index 3f5fd7fa1..cc4462771 100644
--- a/glue/config.py
+++ b/glue/config.py
@@ -249,10 +249,12 @@ class QtToolRegistry(Registry):
 
     def __init__(self):
         self._members = {}
+        self._lazy_members = []
         self._loaded = False
 
     @property
     def members(self):
+        self._load_lazy_members()
         if not self._loaded:
             defaults = self.default_members()
             for key in defaults:
diff --git a/glue/plugins/__init__.py b/glue/plugins/__init__.py
index e16f3da34..d18b8ca65 100644
--- a/glue/plugins/__init__.py
+++ b/glue/plugins/__init__.py
@@ -6,6 +6,8 @@ def register_plugins():
     qt_client.lazy_add('glue.plugins.ginga_viewer')
     exporters.lazy_add('glue.plugins.export_d3po')
     exporters.lazy_add('glue.plugins.export_plotly')
+    exporters.lazy_add('glue.plugins.tools.pv_slicer')
+    exporters.lazy_add('glue.plugins.tools.spectrum_tool')
 
 
 def load_plugin(plugin):
@@ -16,7 +18,7 @@ def load_plugin(plugin):
     # import importlib
     # module = importlib.import_module(plugin)
     __import__(plugin)
-    return sys.modules[plugin]
+    module = sys.modules[plugin]
     if hasattr(module, 'setup'):
         module.setup()
     else:
diff --git a/glue/plugins/tools/pv_slicer.py b/glue/plugins/tools/pv_slicer.py
index bb67d0559..9e5542f81 100644
--- a/glue/plugins/tools/pv_slicer.py
+++ b/glue/plugins/tools/pv_slicer.py
@@ -4,6 +4,14 @@
 from ...qt.widgets.mpl_widget import defer_draw
 
 
+def setup():
+    from ...logger import logger
+    from ...config import tool_registry
+    from ...qt.widgets import ImageWidget
+    tool_registry.add(PVSlicerTool, widget_cls=ImageWidget)
+    logger.info("Loaded pv slicer plugin")
+
+
 class PVSlicerTool(object):
 
     def __init__(self, widget=None):
diff --git a/glue/plugins/tools/spectrum_tool.py b/glue/plugins/tools/spectrum_tool.py
index 19aa92f0e..d511cb9a9 100644
--- a/glue/plugins/tools/spectrum_tool.py
+++ b/glue/plugins/tools/spectrum_tool.py
@@ -33,6 +33,14 @@
 from ...utils import drop_axis
 
 
+def setup():
+    from ...logger import logger
+    from ...config import tool_registry
+    from ...qt.widgets import ImageWidget
+    tool_registry.add(SpectrumTool, widget_cls=ImageWidget)
+    logger.info("Loaded spectrum tool plugin")
+
+
 class Extractor(object):
     # Warning:
     # Coordinate conversion is not well-defined if pix2world is not
diff --git a/glue/qt/widgets/image_widget.py b/glue/qt/widgets/image_widget.py
index 00ac0f53c..0e8bf8825 100644
--- a/glue/qt/widgets/image_widget.py
+++ b/glue/qt/widgets/image_widget.py
@@ -88,9 +88,7 @@ def make_toolbar(self):
 
     @staticmethod
     def _get_default_tools():
-        from ...plugins.tools.pv_slicer import PVSlicerTool
-        from ...plugins.tools.spectrum_tool import SpectrumTool
-        return [PVSlicerTool, SpectrumTool]
+        return []
 
     def _setup_tools(self):
         """