Raise a meaningful exception.

pisi/db/repodb.py

@@ -21,6 +21,9 @@ import pisi.index
 import pisi.context as ctx
 import pisi.db.lazydb as lazydb
 
+class RepoError(pisi.Error):
+    pass
+
 class Repo:
     def __init__(self, indexuri):
         self.indexuri = indexuri
@@ -109,7 +112,10 @@ class RepoDB(lazydb.LazyDB):
         if index_path.endswith("bz2"):
             index_path = index_path.split(".bz2")[0]
 
-        return piksemel.parse(index_path)
+        try:
+            return piksemel.parse(index_path)
+        except Exception, e:
+            raise RepoError("Error parsing repository index information. Index file does not exist or is malformed.")
 
     def get_repo(self, repo):
         return Repo(pisi.uri.URI(self.get_repo_url(repo)))