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.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@10193 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/template/defaultfilters.py

@@ -515,12 +515,18 @@ last.is_safe = True
 
 def length(value):
     """Returns the length of the value - useful for lists."""
-    return len(value)
+    try:
+        return len(value)
+    except (ValueError, TypeError):
+        return ''
 length.is_safe = True
 
 def length_is(value, arg):
     """Returns a boolean of whether the value's length is the argument."""
-    return len(value) == int(arg)
+    try:
+        return len(value) == int(arg)
+    except (ValueError, TypeError):
+        return ''
 length_is.is_safe = False
 
 def random(value):