silent_variable_failure not suppressing exception during dict lookup

[Thomas Steinacher <tom@…>]

Example:

from django.template import Context, Template

class E(Exception): silent_variable_failure = True

class A(object):
	def __getitem__(self, key):
		raise E

t = Template("{{ a.b }}")

t.render(Context({"a": A()}))

According to Django docs, the exception should be suppresed and an empty string should be returned. However, instead, Django raises the exception:

---------------------------------------------------------------------------
TemplateSyntaxError                       Traceback (most recent call last)

/home/user/user/<ipython console> in <module>()

/usr/lib/python2.5/site-packages/django/template/__init__.pyc in render(self, context)
    176     def render(self, context):
    177         "Display stage -- can be called many times"
--> 178         return self.nodelist.render(context)
    179 
    180 def compile_string(template_string, origin):

/usr/lib/python2.5/site-packages/django/template/__init__.pyc in render(self, context)
    777         for node in self:
    778             if isinstance(node, Node):
--> 779                 bits.append(self.render_node(node, context))
    780             else:
    781                 bits.append(node)

/usr/lib/python2.5/site-packages/django/template/debug.py in render_node(self, node, context)
     79             wrapped.source = node.source
     80             wrapped.exc_info = exc_info()
---> 81             raise wrapped
     82         return result
     83 

TemplateSyntaxError: Caught an exception while rendering: 

Original Traceback (most recent call last):
  File "/usr/lib/python2.5/site-packages/django/template/debug.py", line 71, in render_node
    result = node.render(context)
  File "/usr/lib/python2.5/site-packages/django/template/debug.py", line 87, in render
    output = force_unicode(self.filter_expression.resolve(context))
  File "/usr/lib/python2.5/site-packages/django/template/__init__.py", line 546, in resolve
    obj = self.var.resolve(context)
  File "/usr/lib/python2.5/site-packages/django/template/__init__.py", line 687, in resolve
    value = self._resolve_lookup(context)
  File "/usr/lib/python2.5/site-packages/django/template/__init__.py", line 713, in _resolve_lookup
    current = current[bit]
  File "<ipython console>", line 4, in __getitem__
E

Proposed patch:

Index: django/template/__init__.py
===================================================================
--- django/template/__init__.py (revision 11929)
+++ django/template/__init__.py (working copy)
@@ -745,11 +745,11 @@
                             TypeError,  # unsubscriptable object
                             ):
                         raise VariableDoesNotExist("Failed lookup for key [%s] in %r", (bit, current)) # missing attribute
-                except Exception, e:
-                    if getattr(e, 'silent_variable_failure', False):
-                        current = settings.TEMPLATE_STRING_IF_INVALID
-                    else:
-                        raise
+            except Exception, e:
+                if getattr(e, 'silent_variable_failure', False):
+                    current = settings.TEMPLATE_STRING_IF_INVALID
+                else:
+                    raise
 
         return current

[b__2@…]

The same error occurs when a variable that doesn't exist is referenced as the argument of a filter
for example:

{% if use_styleId|default_if_none:my_styleId %}

The stack trace shows the problem to be the naked call to resolve at around line 576:

arg_vals.append(arg.resolve(context))

My quick fix was to duplicate much of the exception logic used in the primary case just above:

                    try:
                        arg_val = arg.resolve(context)
                    except VariableDoesNotExist:
                        if ignore_failures:
                            arg_val = None
                        else:
                            if settings.TEMPLATE_STRING_IF_INVALID:
                                global invalid_var_format_string
                                if invalid_var_format_string is None:
                                    invalid_var_format_string = '%s' in settings.TEMPLATE_STRING_IF_INVALID
                                if invalid_var_format_string:
                                    arg_val= settings.TEMPLATE_STRING_IF_INVALID % self.var
                                else:
                                    arg_val= settings.TEMPLATE_STRING_IF_INVALID
                            else:
                                arg_val = settings.TEMPLATE_STRING_IF_INVALID
                    arg_vals.append(arg_val)

However, it seems to me that Variable.resolve() should be taking care of the settings.TEMPLATE_STRING_IF_INVALID semantic, not FilterExpression.
The patch suggested doesn't seem to do anything since VariableDoesNotExist is not derived from ObjectDoesNotExist. I did not use it.

[b__2@…]

I realized I wasn't working from the trunk. Here is a real proposed patch:

===================================================================
--- __init__.py	(revision 12610)
+++ __init__.py	(working copy)
@@ -583,7 +583,24 @@
                 if not lookup:
                     arg_vals.append(mark_safe(arg))
                 else:
-                    arg_vals.append(arg.resolve(context))
+                    #arg_vals.append(arg.resolve(context))
+                    try:
+                        arg_val = arg.resolve(context)
+                    except VariableDoesNotExist:
+                        if ignore_failures:
+                            arg_val = None
+                        else:
+                            if settings.TEMPLATE_STRING_IF_INVALID:
+                                global invalid_var_format_string
+                                if invalid_var_format_string is None:
+                                    invalid_var_format_string = '%s' in settings.TEMPLATE_STRING_IF_INVALID
+                                if invalid_var_format_string:
+                                    arg_val= settings.TEMPLATE_STRING_IF_INVALID % self.var
+                                else:
+                                    arg_val= settings.TEMPLATE_STRING_IF_INVALID
+                            else:
+                                arg_val = settings.TEMPLATE_STRING_IF_INVALID
+                    arg_vals.append(arg_val)                  
             if getattr(func, 'needs_autoescape', False):

Here is a test case:
>>> from django.template import Context, Template
>>> t = Template("{{'test'|default:notreal}}")
>>> t.render(Context())
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/opt/local/OnQueue2/OQTools/pythonlib/trunk/django/template/__init__.py", line 184, in render
    return self._render(context)
  File "/opt/local/OnQueue2/OQTools/pythonlib/trunk/django/template/__init__.py", line 178, in _render
    return self.nodelist.render(context)
  File "/opt/local/OnQueue2/OQTools/pythonlib/trunk/django/template/__init__.py", line 799, in render
    bits.append(self.render_node(node, context))
  File "/opt/local/OnQueue2/OQTools/pythonlib/trunk/django/template/debug.py", line 82, in render_node
    raise wrapped
TemplateSyntaxError: Caught an exception while rendering: Failed lookup for key [notreal] in u'[{}]'

[Colin Copeland]

add b2's patch

[Colin Copeland]

add patch with tests

[Karen Tracey]

This looks to me like two different problems: the problem in the original description regarding an exception with silent_variable_failure=True not being silenced, and a different problem with non-existent variables passed to filters raising exceptions. I'd like to narrow the focus of this ticket to the first problem, which seems clearly wrong. (I'm less sure of what the right behavior is supposed to be for the 2nd situation.)

[Colin Copeland]

Only dict lookup fix and test

[Colin Copeland]

Since we're not sure what should happen in the template filter scenario, I opened #13167.

[Karen Tracey]

(In [12823]) Fixed #12554: Silence exceptions that have specified silent_variable_failure=True. Thanks Thomas Steinacher, copelco, mlavin.

[Karen Tracey]

(In [12824]) [1.1.X] Fixed #12554: Silence exceptions that have specified silent_variable_failure=True. Thanks Thomas Steinacher, copelco, mlavin.

r12823 from trunk.

[anonymous]

When I do this:

from django.template import Context, Template
from myapp.models import MyModel

MyModel(models.Model):
    some = model.OneToOneField(AnotherModel)

obj = MyModel.objects.get(id=1)

t = Template("{{ obj.some }}")

t.render(Context({"obj": obj}))

Django raises the exception:

---------------------------------------------------------------------------
TemplateSyntaxError                       Traceback (most recent call last)

/home/alejandro/inmegen/<ipython console> in <module>()

/usr/lib/python2.6/site-packages/django/template/__init__.pyc in render(self, context)
    169         context.render_context.push()
    170         try:
--> 171             return self._render(context)
    172         finally:
    173             context.render_context.pop()

/usr/lib/python2.6/site-packages/django/template/__init__.pyc in _render(self, context)
    163 
    164     def _render(self, context):
--> 165         return self.nodelist.render(context)
    166 
    167     def render(self, context):

/usr/lib/python2.6/site-packages/django/template/__init__.pyc in render(self, context)
    795         for node in self:
    796             if isinstance(node, Node):
--> 797                 bits.append(self.render_node(node, context))
    798             else:
    799                 bits.append(node)

TemplateSyntaxError: Caught DoesNotExist while rendering: AnotherModel matching query does not exist.

Proposed patch:

Index: django/template/__init__.py
===================================================================
--- django/template/__init__.py	(revision 12823)
+++ django/template/__init__.py	(working copy)
@@ -745,6 +745,11 @@
                             TypeError,  # unsubscriptable object
                             ):
                         raise VariableDoesNotExist("Failed lookup for key [%s] in %r", (bit, current)) # missing attribute
+                except Exception, e:
+                    if getattr(e, 'silent_variable_failure', False):
+                        current = settings.TEMPLATE_STRING_IF_INVALID
+                    else:
+                        raise
             except Exception, e:
                 if getattr(e, 'silent_variable_failure', False):
                     current = settings.TEMPLATE_STRING_IF_INVALID

[Karen Tracey]

(In [12834]) Fixed #12554 again: Corrected regression in silencing attribute lookups introduced in r12823, plus added a test for this so it doesn't regress again.

[Karen Tracey]

(In [12835]) [1.1.X] Fixed #12554 again: Corrected regression in silencing attribute lookups introduced in r12824, plus added a test for this so it doesn't regress again.

r12834 from trunk.

[Jacob]

Milestone 1.2 deleted