Improved user-facing messages

pending_manager.py

Index: pending_manager.py
diff --git a/pending_manager.py b/pending_manager.py
index 7548be2e2490eae993d80d98a51ed6c49a320d50..2ccdab67836892d3cc6ab7e7bd14b416c8f663af 100644
--- a/pending_manager.py
+++ b/pending_manager.py
@@ -23,10 +23,10 @@ import traceback
 import urllib2
 
 import find_depot_tools  # pylint: disable=W0611
-import checkout
-import git_cl
-import patch
-import subprocess2
+import checkout  # pylint: disable=F0401
+import git_cl  # pylint: disable=F0401
+import patch  # pylint: disable=F0401
+import subprocess2  # pylint: disable=F0401
 
 import errors
 import model
@@ -148,14 +148,18 @@ class PendingManager(object):
   # Delay (secs) between commit bursts.
   COMMIT_BURST_DELAY = 10*60
 
-  def __init__(self, context_obj, pre_patch_verifiers, verifiers):
+  def __init__(self, context_obj, pre_patch_verifiers, verifiers,
+               project_name=''):
     """
     Args:
       pre_patch_verifiers: Verifiers objects that are run before applying the
                            patch.
       verifiers: Verifiers object run after applying the patch.
     """
-    assert len(pre_patch_verifiers) or len(verifiers)
+    if not(len(pre_patch_verifiers) or len(verifiers)):
+      raise ValueError('at least one verifier should be defined (in project %s)'
+                       % project_name)
+
     self.context = context_obj
     self.pre_patch_verifiers = pre_patch_verifiers or []
     self.verifiers = verifiers or []
@@ -429,6 +433,7 @@ class PendingManager(object):
             'Failed to set the flag to False for %s with message %s' % (
               pending.pending_name(), message))
         traceback.print_stack()
+        logging.error(str(e))
         errors.send_stack(e)
       if message:
         try: