}]
 
     def _login(self):
-        (username, password) = self._get_login_info()
+        username, password = self._get_login_info()
         if username is None:
             return
 
             post_url = urljoin(self._LOGIN_URL, post_url)
 
         response = self._download_webpage(
-            post_url, None, 'Logging in as %s' % username,
+            post_url, None, 'Logging in',
             data=urlencode_postdata(login_form), headers={
                 'Referer': self._LOGIN_URL,
             })
 
         if all(p not in response for p in ('>Logout<', 'href="/users/sign_out"')):
             error = self._search_regex(
-                r'<p class="alert alert-danger">(.+?)</p>',
-                response, 'error', default=None)
+                r'<p[^>]+\bclass=(["\'])(?:(?!\1).)*\balert\b(?:(?!\1).)*\1[^>]*>(?P<error>.+?)</p>',
+                response, 'error', default=None, group='error')
             if error:
                 raise ExtractorError('Unable to login: %s' % error, expected=True)
             raise ExtractorError('Unable to log in')