Handle missing dnspython by displaying a warning message

certbot/plugins/manual.py

@@ -15,6 +15,7 @@ import zope.interface
 from functools import partial
 
 from acme import challenges
+from acme import errors as acme_errors
 
 from certbot import errors
 from certbot import interfaces
@@ -213,9 +214,15 @@ s.serve_forever()" """
                                               response=response)
             self._ip_logging_permission(formated_message)
 
-        if not response.simple_verify(
+        try:
+            verification_status = response.simple_verify(
                 achall.chall, achall.domain,
-                achall.account_key.public_key()):
+                achall.account_key.public_key())
+        except acme_errors.DependencyError:
+            verification_status = False
+            logger.warning("Dns challenge requires `dnspython`")
+
+        if not verification_status:
             logger.warning("Self-verify of challenge failed.")
 
         return response

certbot/plugins/manual_test.py

@@ -5,6 +5,7 @@ import unittest
 import mock
 
 from acme import challenges
+from acme import errors as acme_errors
 from acme import jose
 
 from certbot import achallenges
@@ -78,6 +79,19 @@ class AuthenticatorTest(unittest.TestCase):
             self.auth.perform(self.achalls)
             self.assertEqual(2, mock_logger.warning.call_count)
 
+    @mock.patch("certbot.plugins.manual.zope.component.getUtility")
+    @mock.patch("acme.challenges.DNS01Response.simple_verify")
+    @mock.patch("six.moves.input")
+    def test_perform_missing_dependency(self, mock_raw_input, mock_verify, mock_interaction):
+        mock_interaction().yesno.return_value = True
+        mock_verify.side_effect = acme_errors.DependencyError()
+
+        with mock.patch("certbot.plugins.manual.logger") as mock_logger:
+            self.auth.perform([self.dns01])
+            self.assertEqual(2, mock_logger.warning.call_count)
+
+        mock_raw_input.assert_called_once_with("Press ENTER to continue")
+
     @mock.patch("certbot.plugins.manual.zope.component.getUtility")
     @mock.patch("certbot.plugins.manual.Authenticator._notify_and_wait")
     def test_disagree_with_ip_logging(self, mock_notify, mock_interaction):