Monkey patch templates only when the panel is used (#12)

Fixes #6. This moves the monkey patching code from the AppConfig to the panel class, so that when the panel is first instantiated, it then does the monkey patching. This allows the app to be installed with the panel disabled without any overhead.

Author: adamchainz

HISTORY.rst

@@ -17,6 +17,8 @@ Pending Release
 * Skip templates as configured in django-debug-toolbar's
   ``SKIP_TEMPLATE_PREFIXES`` setting
   (`PR #11 <https://github.com/node13h/django-debug-toolbar-template-profiler/pull/11>`__).
+* Only monkey patch ``Template.render()`` methods if the panel is in use
+  (`PR #12 <https://github.com/node13h/django-debug-toolbar-template-profiler/pull/12>`__).
 
 1.0.2 (2017-05-03)
 ------------------

template_profiler_panel/apps.py

@@ -1,52 +1,6 @@
-import inspect
-from time import time
-
-import wrapt
 from django.apps import AppConfig
 
-from template_profiler_panel.signals import template_rendered
-
 
 class TemplateProfilerPanelAppConfig(AppConfig):
     name = "template_profiler_panel"
     verbose_name = "Debug Toolbar Template Profiler Panel"
-
-    def ready(self):
-        self.monkey_patch_template_classes()
-
-    def monkey_patch_template_classes(self):
-        from django.template import Template as DjangoTemplate
-        template_classes = [DjangoTemplate]
-
-        try:
-            from jinja2 import Template as Jinja2Template
-        except ImportError:
-            pass
-        else:
-            template_classes.append(Jinja2Template)
-
-        @wrapt.decorator
-        def render_wrapper(wrapped, instance, args, kwargs):
-            start = time()
-            result = wrapped(*args, **kwargs)
-            end = time()
-
-            stack_depth = 1
-            current_frame = inspect.currentframe()
-            while True:
-                current_frame = current_frame.f_back
-                if current_frame is None:
-                    break
-                stack_depth += 1
-
-            template_rendered.send(
-                sender=instance.__class__,
-                instance=instance,
-                start=start,
-                end=end,
-                level=stack_depth,
-            )
-            return result
-
-        for template_class in template_classes:
-            template_class.render = render_wrapper(template_class.render)

template_profiler_panel/panels/template.py

@@ -1,12 +1,16 @@
+import inspect
 from collections import defaultdict
+from time import time
 
-from django.conf import settings
+import wrapt
+from django.dispatch import Signal
 from django.utils.translation import ugettext_lazy as _
 
 from debug_toolbar.panels import Panel
 from debug_toolbar.panels.sql.utils import contrasting_color_generator
 
-from template_profiler_panel.signals import template_rendered
+
+template_rendered = Signal(providing_args=['instance', 'start', 'end', 'level'])
 
 
 class TemplateProfilerPanel(Panel):
@@ -23,8 +27,56 @@ def __init__(self, *args, **kwargs):
         self.t_min = 0
         self.t_max = 0
         self.total = 0
+        self.monkey_patch_template_classes()
+        self.is_enabled = False
+        template_rendered.connect(self.record)
         super(TemplateProfilerPanel, self).__init__(*args, **kwargs)
 
+    have_monkey_patched_template_classes = False
+
+    @classmethod
+    def monkey_patch_template_classes(cls):
+        if cls.have_monkey_patched_template_classes:
+            return
+
+        from django.template import Template as DjangoTemplate
+        template_classes = [DjangoTemplate]
+
+        try:
+            from jinja2 import Template as Jinja2Template
+        except ImportError:
+            pass
+        else:
+            template_classes.append(Jinja2Template)
+
+        @wrapt.decorator
+        def render_wrapper(wrapped, instance, args, kwargs):
+            start = time()
+            result = wrapped(*args, **kwargs)
+            end = time()
+
+            stack_depth = 1
+            current_frame = inspect.currentframe()
+            while True:
+                current_frame = current_frame.f_back
+                if current_frame is None:
+                    break
+                stack_depth += 1
+
+            template_rendered.send(
+                sender=instance.__class__,
+                instance=instance,
+                start=start,
+                end=end,
+                level=stack_depth,
+            )
+            return result
+
+        for template_class in template_classes:
+            template_class.render = render_wrapper(template_class.render)
+
+        cls.have_monkey_patched_template_classes = True
+
     @property
     def nav_title(self):
         return _('Template Profiler')
@@ -41,9 +93,11 @@ def title(self):
     def _get_color(self, level):
         return self.colors.setdefault(level, next(self.color_generator))
 
-    def record(self, sender, instance, start, end, level, **kwargs):
-        template_name = instance.name
+    def record(self, instance, start, end, level, **kwargs):
+        if not self.enabled:
+            return
 
+        template_name = instance.name
         # Logic copied from django-debug-toolbar:
         # https://github.com/jazzband/django-debug-toolbar/blob/5d095f66fde8f10b45a93c0b35be0a85762b0458/debug_toolbar/panels/templates/panel.py#L77
         is_skipped_template = isinstance(template_name, str) and (
@@ -69,10 +123,10 @@ def record(self, sender, instance, start, end, level, **kwargs):
         })
 
     def enable_instrumentation(self):
-        template_rendered.connect(self.record)
+        self.is_enabled = True
 
     def disable_instrumentation(self):
-        template_rendered.disconnect(self.record)
+        self.is_enabled = False
 
     def _calc_p(self, part, whole):
         return (part / whole) * 100.0