Workaround the fact that pylint calls sys.exit().

presubmit_canned_checks.py

 # Copyright (c) 2010 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Generic presubmit checks that can be reused by other presubmit checks."""
 
 ### Description checks
 
 def CheckChangeHasTestField(input_api, output_api):
   """Requires that the changelist have a TEST= field."""
@@ skipping 476 matching lines @@
           dirnames.remove(item)
       for item in filenames:
         filepath = input_api.os_path.join(dirpath, item)
         if Find(filepath, white_list) and not Find(filepath, black_list):
           files.append(filepath)
 
     # Now that at least one python file was modified and all the python files
     # were listed, try to run pylint.
     try:
       from pylint import lint
-      if lint.Run(sorted(files)):
-        return [output_api.PresubmitPromptWarning('Fix pylint errors first.')]
-      return []
+      result = lint.Run(sorted(files))
+    except SystemExit, e:
+      # pylint has the bad habit of calling sys.exit(), trap it here.
+      result = e.code
     except ImportError:
       if input_api.platform == 'win32':
         return [output_api.PresubmitNotifyResult(
           'Warning: Can\'t run pylint because it is not installed. Please '
           'install manually\n'
           'Cannot do static analysis of python files.')]
       return [output_api.PresubmitError(
           'Please install pylint with "sudo apt-get install python-setuptools; '
           'sudo easy_install pylint"\n'
           'Cannot do static analysis of python files.')]
+    if result:
+      return [output_api.PresubmitPromptWarning('Fix pylint errors first.')]
+    return []
   finally:
     warnings.filterwarnings('default', category=DeprecationWarning)
 
 
 def CheckRietveldTryJobExecution(input_api, output_api, host_url, platforms,
                                  owner):
   if not input_api.is_committing:
     return []
   if not input_api.change.issue or not input_api.change.patchset:
     return []
@@ skipping 67 matching lines @@
     pending_builds_len = len(builder.get('pending_builds', []))
     if pending_builds_len > max_pendings:
       out.append('%s has %d build(s) pending' %
                   (builder_name, pending_builds_len))
   if out:
     return [output_api.PresubmitPromptWarning(
         'Build(s) pending. It is suggested to wait that no more than %d '
             'builds are pending.' % max_pendings,
         long_text='\n'.join(out))]
   return []