Move the logic to load panels inside the DebugToolbar class.

This has the additional advantage of eliminating a side-effect that
happened at import time unnecessarily.

It justified refactoring the way we handle settings and defaults.

9 files changed, 78 insertions, 69 deletions

diff --git a/debug_toolbar/middleware.py b/debug_toolbar/middleware.py
index 80e8ae0..44d0700 100644
--- a/debug_toolbar/middleware.py
+++ b/debug_toolbar/middleware.py
@@ -12,7 +12,7 @@ from django.shortcuts import render
 from django.utils.encoding import force_text
 
 from debug_toolbar.toolbar import DebugToolbar
-from debug_toolbar.utils.settings import CONFIG
+from debug_toolbar.utils import settings as dt_settings
 
 _HTML_TYPES = ('text/html', 'application/xhtml+xml')
 # Handles python threading module bug - http://bugs.python.org/issue14308
@@ -52,10 +52,10 @@ class DebugToolbarMiddleware(object):
 
     def __init__(self):
         # The method to call to decide to show the toolbar
-        self.show_toolbar = CONFIG['SHOW_TOOLBAR_CALLBACK'] or show_toolbar
+        self.show_toolbar = dt_settings.CONFIG['SHOW_TOOLBAR_CALLBACK'] or show_toolbar
 
         # The tag to attach the toolbar to
-        self.tag = '</%s>' % CONFIG['TAG']
+        self.tag = '</%s>' % dt_settings.CONFIG['TAG']
 
     def process_request(self, request):
         __traceback_hide__ = True                                       # noqa
diff --git a/debug_toolbar/models.py b/debug_toolbar/models.py
index d39e7ec..a204b13 100644
--- a/debug_toolbar/models.py
+++ b/debug_toolbar/models.py
@@ -5,7 +5,6 @@ from django.conf.urls import include, patterns, url
 from django.core.urlresolvers import reverse, NoReverseMatch
 from django.utils.importlib import import_module
 
-from debug_toolbar.toolbar import load_panel_classes
 from debug_toolbar.middleware import DebugToolbarMiddleware
 
 
@@ -59,7 +58,3 @@ if settings.DEBUG:
     patch_internal_ips()
     patch_middleware_classes()
     patch_root_urlconf()
-
-
-if is_toolbar_middleware_installed():
-    load_panel_classes()
diff --git a/debug_toolbar/panels/cache.py b/debug_toolbar/panels/cache.py
index 831eacb..7d42c1f 100644
--- a/debug_toolbar/panels/cache.py
+++ b/debug_toolbar/panels/cache.py
@@ -16,7 +16,7 @@ from django.utils.translation import ugettext_lazy as _, ungettext
 from debug_toolbar.panels import DebugPanel
 from debug_toolbar.utils import (tidy_stacktrace, render_stacktrace,
                                  get_template_info, get_stack)
-from debug_toolbar.utils.settings import CONFIG
+from debug_toolbar.utils import settings as dt_settings
 
 
 cache_called = Signal(providing_args=[
@@ -29,7 +29,7 @@ def send_signal(method):
         value = method(self, *args, **kwargs)
         t = time.time() - t
 
-        if CONFIG['ENABLE_STACKTRACES']:
+        if dt_settings.CONFIG['ENABLE_STACKTRACES']:
             stacktrace = tidy_stacktrace(reversed(get_stack()))
         else:
             stacktrace = []
diff --git a/debug_toolbar/panels/signals.py b/debug_toolbar/panels/signals.py
index 3dd035a..1d24b80 100644
--- a/debug_toolbar/panels/signals.py
+++ b/debug_toolbar/panels/signals.py
@@ -16,7 +16,7 @@ except ImportError:
     connection_created = None
 
 from debug_toolbar.panels import DebugPanel
-from debug_toolbar.utils.settings import CONFIG
+from debug_toolbar.utils import settings as dt_settings
 
 
 class SignalDebugPanel(DebugPanel):
@@ -63,7 +63,7 @@ class SignalDebugPanel(DebugPanel):
     @property
     def signals(self):
         signals = self.SIGNALS.copy()
-        for signal in CONFIG['EXTRA_SIGNALS']:
+        for signal in dt_settings.CONFIG['EXTRA_SIGNALS']:
             mod_path, signal_name = signal.rsplit('.', 1)
             signals_mod = import_module(mod_path)
             signals[signal_name] = getattr(signals_mod, signal_name)
diff --git a/debug_toolbar/panels/template.py b/debug_toolbar/panels/template.py
index 172765a..d918cd7 100644
--- a/debug_toolbar/panels/template.py
+++ b/debug_toolbar/panels/template.py
@@ -15,7 +15,7 @@ from django.utils.translation import ugettext_lazy as _
 
 from debug_toolbar.panels import DebugPanel
 from debug_toolbar.utils.tracking.db import recording, SQLQueryTriggered
-from debug_toolbar.utils.settings import CONFIG
+from debug_toolbar.utils import settings as dt_settings
 
 # Code taken and adapted from Simon Willison and Django Snippets:
 # http://www.djangosnippets.org/snippets/766/
@@ -140,7 +140,7 @@ class TemplateDebugPanel(DebugPanel):
                 template.origin_name = 'No origin'
             info['template'] = template
             # Clean up context for better readability
-            if CONFIG['SHOW_TEMPLATE_CONTEXT']:
+            if dt_settings.CONFIG['SHOW_TEMPLATE_CONTEXT']:
                 context_list = template_data.get('context', [])
                 info['context'] = '\n'.join(context_list)
             template_context.append(info)
diff --git a/debug_toolbar/toolbar.py b/debug_toolbar/toolbar.py
index c0c210f..32dc1b7 100644
--- a/debug_toolbar/toolbar.py
+++ b/debug_toolbar/toolbar.py
@@ -5,11 +5,12 @@ The main DebugToolbar class that loads and renders the Toolbar.
 from __future__ import unicode_literals
 
 from django.conf import settings
+from django.core.exceptions import ImproperlyConfigured
 from django.template.loader import render_to_string
 from django.utils.datastructures import SortedDict
 from django.utils.importlib import import_module
 
-from debug_toolbar.utils.settings import CONFIG
+from debug_toolbar.utils import settings as dt_settings
 
 
 class DebugToolbar(object):
@@ -19,7 +20,7 @@ class DebugToolbar(object):
         self._panels = SortedDict()
         base_url = self.request.META.get('SCRIPT_NAME', '')
         self.config = {}
-        self.config.update(CONFIG)
+        self.config.update(dt_settings.CONFIG)
         self.template_context = {
             'BASE_URL': base_url,  # for backwards compatibility
             'STATIC_URL': settings.STATIC_URL,
@@ -40,8 +41,7 @@ class DebugToolbar(object):
         """
         Populate debug panels
         """
-        global panel_classes
-        for panel_class in panel_classes:
+        for panel_class in self.get_panel_classes():
             panel_instance = panel_class(self, context=self.template_context)
             self._panels[panel_class] = panel_instance
 
@@ -65,7 +65,7 @@ class DebugToolbar(object):
         cls = type(self)
         cls._counter += 1
         cls._storage[cls._counter] = self
-        for _ in range(len(cls._storage) - CONFIG['RESULTS_CACHE_SIZE']):
+        for _ in range(len(cls._storage) - dt_settings.CONFIG['RESULTS_CACHE_SIZE']):
             # When we drop support for Python 2.6 and switch to
             # collections.OrderedDict, use popitem(last=False).
             del cls._storage[cls._storage.keyOrder[0]]
@@ -75,45 +75,35 @@ class DebugToolbar(object):
     def fetch(cls, storage_id):
         return cls._storage.get(storage_id)
 
+    # Manually implement class-level caching of the list of panels because
+    # it's more obvious than going through an abstraction.
 
+    _panel_classes = None
 
-panel_classes = []
-
-
-def load_panel_classes():
-    from django.conf import settings
-    from django.core.exceptions import ImproperlyConfigured
-
-    # Check if settings has a DEBUG_TOOLBAR_PANELS, otherwise use default
-    panels = getattr(settings, 'DEBUG_TOOLBAR_PANELS', (
-        'debug_toolbar.panels.version.VersionDebugPanel',
-        'debug_toolbar.panels.timer.TimerDebugPanel',
-        'debug_toolbar.panels.settings_vars.SettingsVarsDebugPanel',
-        'debug_toolbar.panels.headers.HeaderDebugPanel',
-        'debug_toolbar.panels.request_vars.RequestVarsDebugPanel',
-        'debug_toolbar.panels.sql.SQLDebugPanel',
-        'debug_toolbar.panels.template.TemplateDebugPanel',
-        'debug_toolbar.panels.cache.CacheDebugPanel',
-        'debug_toolbar.panels.signals.SignalDebugPanel',
-        'debug_toolbar.panels.logger.LoggingPanel',
-    ))
-    for panel_path in panels:
-        try:
-            dot = panel_path.rindex('.')
-        except ValueError:
-            raise ImproperlyConfigured(
-                "%s isn't a debug panel module" % panel_path)
-        panel_module, panel_classname = panel_path[:dot], panel_path[dot + 1:]
-        try:
-            mod = import_module(panel_module)
-        except ImportError as e:
-            raise ImproperlyConfigured(
-                'Error importing debug panel %s: "%s"' %
-                (panel_module, e))
-        try:
-            panel_class = getattr(mod, panel_classname)
-        except AttributeError:
-            raise ImproperlyConfigured(
-                'Toolbar Panel module "%s" does not define a "%s" class' %
-                (panel_module, panel_classname))
-        panel_classes.append(panel_class)
+    @classmethod
+    def get_panel_classes(cls):
+        if cls._panel_classes is None:
+            # Load panels in a temporary variable for thread safety.
+            panel_classes = []
+            for panel_path in dt_settings.PANELS:
+                # This logic could be replaced with import_by_path in Django 1.6.
+                try:
+                    panel_module, panel_classname = panel_path.rsplit('.', 1)
+                except ValueError:
+                    raise ImproperlyConfigured(
+                        "%s isn't a debug panel module" % panel_path)
+                try:
+                    mod = import_module(panel_module)
+                except ImportError as e:
+                    raise ImproperlyConfigured(
+                        'Error importing debug panel %s: "%s"' %
+                        (panel_module, e))
+                try:
+                    panel_class = getattr(mod, panel_classname)
+                except AttributeError:
+                    raise ImproperlyConfigured(
+                        'Toolbar Panel module "%s" does not define a "%s" class' %
+                        (panel_module, panel_classname))
+                panel_classes.append(panel_class)
+            cls._panel_classes = panel_classes
+        return cls._panel_classes
diff --git a/debug_toolbar/utils/settings.py b/debug_toolbar/utils/settings.py
index 12dc231..45f661f 100644
--- a/debug_toolbar/utils/settings.py
+++ b/debug_toolbar/utils/settings.py
@@ -4,6 +4,13 @@ from django.conf import settings
 from django.utils import six
 
 
+# Always import this module as follows:
+# from debug_toolbar.utils import settings [as dt_settings]
+
+# Don't import directly CONFIG or PANELs, or you will miss changes performed
+# with override_settings in tests.
+
+
 CONFIG_DEFAULTS = {
     'INTERCEPT_REDIRECTS': False,
     'SHOW_TOOLBAR_CALLBACK': None,
@@ -27,3 +34,20 @@ CONFIG_DEFAULTS = {
 CONFIG = {}
 CONFIG.update(CONFIG_DEFAULTS)
 CONFIG.update(getattr(settings, 'DEBUG_TOOLBAR_CONFIG', {}))
+
+
+PANELS_DEFAULTS = (
+    'debug_toolbar.panels.version.VersionDebugPanel',
+    'debug_toolbar.panels.timer.TimerDebugPanel',
+    'debug_toolbar.panels.settings_vars.SettingsVarsDebugPanel',
+    'debug_toolbar.panels.headers.HeaderDebugPanel',
+    'debug_toolbar.panels.request_vars.RequestVarsDebugPanel',
+    'debug_toolbar.panels.sql.SQLDebugPanel',
+    'debug_toolbar.panels.template.TemplateDebugPanel',
+    'debug_toolbar.panels.cache.CacheDebugPanel',
+    'debug_toolbar.panels.signals.SignalDebugPanel',
+    'debug_toolbar.panels.logger.LoggingPanel',
+)
+
+
+PANELS = getattr(settings, 'DEBUG_TOOLBAR_PANELS', PANELS_DEFAULTS)
diff --git a/debug_toolbar/utils/tracking/db.py b/debug_toolbar/utils/tracking/db.py
index 157334a..fd56ff9 100644
--- a/debug_toolbar/utils/tracking/db.py
+++ b/debug_toolbar/utils/tracking/db.py
@@ -11,7 +11,7 @@ from django.utils.encoding import force_text
 from django.utils import six
 
 from debug_toolbar.utils import tidy_stacktrace, get_template_info, get_stack
-from debug_toolbar.utils.settings import CONFIG
+from debug_toolbar.utils import settings as dt_settings
 
 
 class SQLQueryTriggered(Exception):
@@ -92,7 +92,7 @@ class NormalCursorWrapper(object):
         finally:
             stop_time = time()
             duration = (stop_time - start_time) * 1000
-            if CONFIG['ENABLE_STACKTRACES']:
+            if dt_settings.CONFIG['ENABLE_STACKTRACES']:
                 stacktrace = tidy_stacktrace(reversed(get_stack()))
             else:
                 stacktrace = []
@@ -135,7 +135,7 @@ class NormalCursorWrapper(object):
                 'stacktrace': stacktrace,
                 'start_time': start_time,
                 'stop_time': stop_time,
-                'is_slow': duration > CONFIG['SQL_WARNING_THRESHOLD'],
+                'is_slow': duration > dt_settings.CONFIG['SQL_WARNING_THRESHOLD'],
                 'is_select': sql.lower().strip().startswith('select'),
                 'template_info': template_info,
             }
diff --git a/tests/__init__.py b/tests/__init__.py
index 0abb8a3..b3b9440 100644
--- a/tests/__init__.py
+++ b/tests/__init__.py
@@ -1,7 +1,7 @@
 # Refresh the debug toolbar's configuration when overriding settings.
 
-from debug_toolbar.utils.settings import CONFIG, CONFIG_DEFAULTS
-from debug_toolbar.toolbar import load_panel_classes, panel_classes  # noqa
+from debug_toolbar.toolbar import DebugToolbar
+from debug_toolbar.utils import settings as dt_settings
 
 from django.dispatch import receiver
 from django.test.signals import setting_changed
@@ -10,13 +10,13 @@ from django.test.signals import setting_changed
 @receiver(setting_changed)
 def update_toolbar_config(**kwargs):
     if kwargs['setting'] == 'DEBUG_TOOLBAR_CONFIG':
-        CONFIG.update(CONFIG_DEFAULTS)
-        CONFIG.update(kwargs['value'] or {})
+        dt_settings.CONFIG = {}
+        dt_settings.CONFIG.update(dt_settings.CONFIG_DEFAULTS)
+        dt_settings.CONFIG.update(kwargs['value'] or {})
 
 
 @receiver(setting_changed)
 def update_toolbar_panels(**kwargs):
     if kwargs['setting'] == 'DEBUG_TOOLBAR_PANELS':
-        global panel_classes
-        panel_classes = []                                              # noqa
-        load_panel_classes()
+        dt_settings.PANELS = kwargs['value'] or dt_settings.PANELS_DEFAULTS
+        DebugToolbar._panel_classes = None