add some error handling to App

cliff/app.py

@@ -59,6 +59,12 @@ class App(object):
             callback=self.show_verbose_help,
             help="show verbose help message and exit",
             )
+        parser.add_option(
+            '--debug', 
+            default=False,
+            action='store_true',
+            help='show tracebacks on errors',
+            )
         return parser
 
     def show_verbose_help(self, *args):
@@ -106,7 +112,7 @@ class App(object):
         """
         return
 
-    def clean_up(self, cmd, result):
+    def clean_up(self, cmd, result, err):
         """Hook run after a command is done to shutdown the app.
         """
         return
@@ -120,9 +126,18 @@ class App(object):
         self.configure_logging()
         cmd_factory, cmd_name, sub_argv = self.command_manager.find_command(remainder)
         cmd = cmd_factory(self, self.options)
-        self.prepare_to_run_command(cmd)
-        cmd_parser = cmd.get_parser(' '.join([self.NAME, cmd_name]))
-        parsed_args = cmd_parser.parse_args(sub_argv)
-        result = cmd.run(parsed_args)
-        self.clean_up(cmd, result)
+        err = None
+        result = 1
+        try:
+            self.prepare_to_run_command(cmd)
+            cmd_parser = cmd.get_parser(' '.join([self.NAME, cmd_name]))
+            parsed_args = cmd_parser.parse_args(sub_argv)
+            result = cmd.run(parsed_args)
+        except Exception as err:
+            if self.options.debug:
+                LOG.exception(err)
+                raise
+            LOG.error(err)
+        finally:
+            self.clean_up(cmd, result, err)
         return result

demoapp/cliffdemo/main.py

@@ -19,14 +19,16 @@ class DemoApp(App):
     def prepare_to_run_command(self, cmd):
         self.log.debug('prepare_to_run_command %s', cmd.__class__.__name__)
 
-    def clean_up(self, cmd, result):
+    def clean_up(self, cmd, result, err):
         self.log.debug('clean_up %s', cmd.__class__.__name__)
+        if err:
+            self.log.debug('got an error: %s', err)
 
 
 def main(argv=sys.argv[1:]):
     myapp = DemoApp()
-    myapp.run(argv)
+    return myapp.run(argv)
 
 
 if __name__ == '__main__':
-    main(sys.argv[1:])
+    sys.exit(main(sys.argv[1:]))

demoapp/cliffdemo/simple.py

@@ -12,3 +12,13 @@ class Simple(Command):
         self.log.info('sending greeting')
         self.log.debug('debugging')
         print('hi!')
+
+
+class Error(Command):
+    "Always raises an error"
+
+    log = logging.getLogger(__name__)
+
+    def run(self, parsed_args):
+        self.log.info('causing error')
+        raise RuntimeError('this is the expected exception')

demoapp/setup.py

@@ -163,6 +163,7 @@ setup(
         'cliff.demo': [
             'simple = cliffdemo.simple:Simple',
             'two_part = cliffdemo.simple:Simple',
+            'error = cliffdemo.simple:Error',
             ],
         # 'virtualenvwrapper.initialize': [
         #     'user_scripts = virtualenvwrapper.user_scripts:initialize',