magic-removal: Removed SilentVariableFailure exception, in favor of a silent_variable_failure attribute on the exception. Updated docs and added unit tests.

git-svn-id: http://code.djangoproject.com/svn/django/branches/magic-removal@1680 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/core/exceptions.py

@@ -1,13 +1,11 @@
 "Global Django exceptions"
 
-from django.core.template import SilentVariableFailure
-
 class Http404(Exception):
     pass
 
-class ObjectDoesNotExist(SilentVariableFailure):
+class ObjectDoesNotExist(Exception):
     "The requested object does not exist"
-    pass
+    silent_variable_failure = True
 
 class SuspiciousOperation(Exception):
     "The user did something suspicious"

django/core/template/__init__.py

@@ -102,10 +102,6 @@ class TemplateDoesNotExist(Exception):
 class VariableDoesNotExist(Exception):
     pass
 
-class SilentVariableFailure(Exception):
-    "Any function raising this exception will be ignored by resolve_variable"
-    pass
-
 class InvalidTemplateLibrary(Exception):
     pass
 
@@ -662,12 +658,15 @@ def resolve_variable(path, context):
                         else:
                             try: # method call (assuming no args required)
                                 current = current()
-                            except SilentVariableFailure:
-                                current = ''
                             except TypeError: # arguments *were* required
                                 # GOTCHA: This will also catch any TypeError
                                 # raised in the function itself.
                                 current = '' # invalid method call
+                            except Exception, e:
+                                if getattr(e, 'silent_variable_failure', False):
+                                    current = ''
+                                else:
+                                    raise
                 except (TypeError, AttributeError):
                     try: # list-index lookup
                         current = current[int(bits[0])]

docs/templates_python.txt

@@ -147,10 +147,10 @@ Method lookups are slightly more complex than the other lookup types. Here are
 some things to keep in mind:
 
     * If, during the method lookup, a method raises an exception, the exception
-      will be propagated, unless the exception subclasses
+      will be propagated, unless the exception has an attribute
-      ``django.core.template.SilentVariableFailure``. If the exception
+      ``silent_variable_failure`` whose value is ``True``. If the exception
-      subclasses ``SilentVariableFailure``, the variable will render as an
+      *does* have a ``silent_variable_failure`` attribute, the variable will
-      empty string. Example::
+      render as an empty string. Example::
 
         >>> t = Template("My name is {{ person.first_name }}.")
         >>> class PersonClass3:
@@ -162,15 +162,21 @@ some things to keep in mind:
         ...
         AssertionError: foo
 
-        >>> from django.core.template import SilentVariableFailure
+        >>> class SilentAssertionError(Exception):
-        >>> class SilentAssertionError(SilentVariableFailure): pass
+        ...     silent_variable_failure = True
         >>> class PersonClass4:
         ...     def first_name(self):
-        ...         raise SilentAssertionError, "foo"
+        ...         raise SilentAssertionError
         >>> p = PersonClass4()
         >>> t.render(Context({"person": p}))
         "My name is ."
 
+      Note that ``django.core.exceptions.ObjectDoesNotExist``, which is the
+      base class for all Django database API ``DoesNotExist`` exceptions, has
+      ``silent_variable_failure = True``. So if you're using Django templates
+      with Django model objects, any ``DoesNotExist`` exception will fail
+      silently.
+
     * A method call will only work if the method has no required arguments.
       Otherwise, the system will move to the next lookup type (list-index
       lookup).

tests/othertests/templates.py

@@ -32,6 +32,12 @@ template.libraries['django.templatetags.testtags'] = register
 # Helper objects for template tests #
 #####################################
 
+class SomeException(Exception):
+    silent_variable_failure = True
+
+class SomeOtherException(Exception):
+    pass
+
 class SomeClass:
     def __init__(self):
         self.otherclass = OtherClass()
@@ -42,6 +48,12 @@ class SomeClass:
     def method2(self, o):
         return o
 
+    def method3(self):
+        raise SomeException
+
+    def method4(self):
+        raise SomeOtherException
+
 class OtherClass:
     def method(self):
         return "OtherClass.method"
@@ -133,7 +145,14 @@ TEMPLATE_TESTS = {
     'basic-syntax31': (r'{{ var|default_if_none:var2 }}', {"var": None, "var2": "happy"}, 'happy'),
 
     # Default argument testing
-    'basic-syntax32' : (r'{{ var|yesno:"yup,nup,mup" }} {{ var|yesno }}', {"var": True}, 'yup yes'),
+    'basic-syntax32': (r'{{ var|yesno:"yup,nup,mup" }} {{ var|yesno }}', {"var": True}, 'yup yes'),
+
+    # Fail silently for methods that raise an exception with a "silent_variable_failure" attribute
+    'basic-syntax33': (r'1{{ var.method3 }}2', {"var": SomeClass()}, "12"),
+
+    # In methods that raise an exception without a "silent_variable_attribute" set to True,
+    # the exception propogates
+    'basic-syntax34': (r'1{{ var.method4 }}2', {"var": SomeClass()}, SomeOtherException),
 
     ### IF TAG ################################################################
     'if-tag01': ("{% if foo %}yes{% else %}no{% endif %}", {"foo": True}, "yes"),