Index: django/template/defaultfilters.py
===================================================================
--- django/template/defaultfilters.py	(revisión: 9768)
+++ django/template/defaultfilters.py	(copia de trabajo)
@@ -507,12 +507,18 @@
 
 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):