Django should not silently ignore AttributeErrors raised in functions called by template

[Thomas Steinacher <tom@…>]

Consider atemplate

{{ obj.some_function }}

where obj's some_function exists but raises an AttributeError because of a bug in the function's code. Django silently ignores the error and displays an empty string instead of a traceback, which could save much time when debugging.

Probably this beahaviour is because Django returns silently if we call an attribute that does not exist. But ideally it should only fail silently if the function does not exist, not if it raises an AttributeError. Therefore Django should first check using getattr() if the function exists and THEN call it, and not catch AttributeError.

[Thomas Steinacher <tom@…>]

Same applies for TypeError.

[Peter Bengtsson]

I created this patch based on 1.2 pre-alpha SVN-11617

Before this patch, inside _resolve_lookup(), it lump together AttributeErrors you get when doing getattr(current, bit) with AttributeErrors you get within current=current() when we in fact should treat them as two different errors. Django templates fail silently, by definition, on lookups that as in "it doesn't exist" but allows errors within propagate once found.

The patch still doesn't solve the problem with TypeErrors. Next patch maybe or a separate ticket.

[Julien Phalip]

See #6907 for a related issue. I was almost tempted to close this one as a dupe.

[Aymeric Augustin]

This is fixed in trunk.

Test 1

In a view, define:

    def foo():
        raise AttributeError

and put foo in the context.

In a template, render:

{{ foo }}

With DEBUG = True you get the debug page.

Test 2

In a view, define:

class MyObj(object):
    def foo(self):
        raise AttributeError
obj = MyObj()

and put obj in the context.

In a template, render:

{{ obj.foo }}

With DEBUG = True you get the debug page.