Fix error when run with no arguments on Python 3

Python 3 changed the map built-in to return an iterable instead of a list.
When tested in a boolean context, this always returns True, even if it
would not return anything when iterated.

Instead of the usage being printed, this error was printed:
ERROR: 'Namespace' object has no attribute 'func'

Use list comprehension instead to ensure that an iterable isn't returned

Change-Id: Ie15f2fa8ee93ab26490e371133fa0f944430737b
Closes-bug: 1295356

novaclient/shell.py

@@ -785,7 +785,8 @@ class OpenStackHelpFormatter(argparse.HelpFormatter):
 
 def main():
     try:
-        OpenStackComputeShell().main(map(strutils.safe_decode, sys.argv[1:]))
+        argv = [strutils.safe_decode(a) for a in sys.argv[1:]]
+        OpenStackComputeShell().main(argv)
 
     except Exception as e:
         logger.debug(e, exc_info=1)

novaclient/tests/test_shell.py

@@ -257,3 +257,17 @@ class ShellTest(utils.TestCase):
     @mock.patch('novaclient.client.Client')
     def test_v_unknown_service_type(self, mock_client):
         self._test_service_type('unknown', 'compute', mock_client)
+
+    @mock.patch('sys.argv', ['nova'])
+    @mock.patch('sys.stdout', six.StringIO())
+    @mock.patch('sys.stderr', six.StringIO())
+    def test_main_noargs(self):
+        # Ensure that main works with no command-line arguments
+        try:
+            novaclient.shell.main()
+        except SystemExit as exc:
+            self.fail('Unexpected SystemExit')
+
+        # We expect the normal usage as a result
+        self.assertIn('Command-line interface to the OpenStack Nova API',
+                      sys.stdout.getvalue())