Add nicer exception reporting inside Templite so when a template goes wrong we have some hope of figuring out why.

2 files changed, 16 insertions, 3 deletions

diff --git a/coverage/templite.py b/coverage/templite.py
index f61fbdc..22c93a9 100644
--- a/coverage/templite.py
+++ b/coverage/templite.py
@@ -2,7 +2,7 @@
 
 # Coincidentally named the same as http://code.activestate.com/recipes/496702/
 
-import re
+import re, sys
 
 class Templite(object):
     """A simple template renderer, for a nano-subset of Django syntax.
@@ -120,7 +120,13 @@ class _TempliteEngine(object):
             if op == 'lit':
                 self.result += args
             elif op == 'exp':
-                self.result += str(self.evaluate(args))
+                try:
+                    self.result += str(self.evaluate(args))
+                except:
+                    exc_class, exc, tb = sys.exc_info()
+                    new_exc = exc_class("Couldn't evaluate {{ %s }}: %s"
+                                        % (args, exc))
+                    raise exc_class, new_exc, tb
             elif op == 'if':
                 expr, body = args
                 if self.evaluate(expr):
diff --git a/test/test_templite.py b/test/test_templite.py
index 8cb2586..6b445aa 100644
--- a/test/test_templite.py
+++ b/test/test_templite.py
@@ -191,6 +191,13 @@ class TempliteTest(unittest.TestCase):
             "@a0b0c0a1b1c1a2b2c2!"
             )
 
-        
+    def test_exception(self):
+        # TypeError: Couldn't evaluate {{ foo.bar.baz }}:
+        # 'NoneType' object is unsubscriptable
+        self.assertRaises(TypeError, self.try_render,
+            "Hey {{foo.bar.baz}} there", {'foo': None}, "Hey XXX there"
+            )
+
+
 if __name__ == '__main__':
     unittest.main()