length and length_is filters don't fail silently

[magneto]

django/template/defaultfilters.py", line 469, in length

if the input object has no len defined, this throws a nasty exception .. given the very large number of time i imagine this is used

would it be proper to simply 'return 0' for non list like things?

in particular the 'with' command is problematic (if 'my_thing' is unresolved, it blows up)

{% with my_thing|length as my_length %}

{% endwith %}

Index: django/template/defaultfilters.py
===================================================================
--- django/template/defaultfilters.py   (revision 8455)
+++ django/template/defaultfilters.py   (working copy)
@@ -466,7 +466,10 @@
 
 def length(value):
     """Returns the length of the value - useful for lists."""
-    return len(value)
+    try:
+        return len(value)
+    except:
+        return 0
 length.is_safe = True
 
 def length_is(value, arg):

[Chris Beaven]

This is also an issue for length_is.

I think returning '' would make more sense for the length filter (it's invalid, not 0)

[Malcolm Tredinnick]

I agree with Chris: if you're applying length or length_is to something that isn't measurable, it's an invalid usage, so returning an empty string is probably better.

[Marcelo Ramos]

Submitted patch which makes both filters to return when their arguments are not measurable.

[Chris Beaven]

Marcelor, if you wouldn't mind extending the template filter test suite to encompass this change then that'll speed up the checkin process.

Oh, and it'd be better style to just catch ValueError and TypeError rather than a raw except.

[Marcelo Ramos]

More specific exception catching.

[Marcelo Ramos]

Fixed bad syntax.

[rob]

keeping the filter diffs and test diffs together

[rob]

i think that takes care of needing tests

[Chris Beaven]

PEP8 pedantry and one more test

[Chris Beaven]

Thanks marcelor and rob. Marking for checkin

[Gary Wilson]

(In [10193]) Fixed #8462 -- Made length and length_is template filters fail silently when given a value that has undefined length and added tests for both filters. Based on patch from marcelor, rob, and SmileyChris.

[Gary Wilson]

(In [10194]) [1.0.X]: Fixed #8462 -- Made length and length_is template filters fail silently when given a value that has undefined length and added tests for both filters. Based on patch from marcelor, rob, and SmileyChris.

Backport of r10193 from trunk.