[mod] pylint: minor code change to allow pylint globally

This commit is only a step, it doesn't fix all the issues reported by pylint

searx/engines/qwant.py

@@ -17,7 +17,7 @@ from searx.utils import html_to_text, match_language
 
 
 # engine dependent config
-categories = None
+categories = []
 paging = True
 language_support = True
 supported_languages_url = 'https://qwant.com/region'

searx/engines/xpath.py

@@ -7,6 +7,7 @@ url_xpath = None
 content_xpath = None
 title_xpath = None
 thumbnail_xpath = False
+categories = []
 paging = False
 suggestion_xpath = ''
 results_xpath = ''

searx/webapp.py

@@ -44,7 +44,7 @@ from urllib.parse import urlencode, urlparse, urljoin, urlsplit
 
 from pygments import highlight
 from pygments.lexers import get_lexer_by_name
-from pygments.formatters import HtmlFormatter
+from pygments.formatters import HtmlFormatter  # pylint: disable=no-name-in-module
 
 from werkzeug.middleware.proxy_fix import ProxyFix
 from flask import (
@@ -111,7 +111,7 @@ app = Flask(
 
 app.jinja_env.trim_blocks = True
 app.jinja_env.lstrip_blocks = True
-app.jinja_env.add_extension('jinja2.ext.loopcontrols')
+app.jinja_env.add_extension('jinja2.ext.loopcontrols')  # pylint: disable=no-member
 app.secret_key = settings['server']['secret_key']
 
 # see https://flask.palletsprojects.com/en/1.1.x/cli/
@@ -565,14 +565,11 @@ def index():
 
         result_container = search.search()
 
-    except Exception as e:
+    except SearxParameterException as e:
-        # log exception
+        logger.exception('search error: SearxParameterException')
-        logger.exception('search error')
-
-        # is it an invalid input parameter or something else ?
-        if (issubclass(e.__class__, SearxParameterException)):
         return index_error(output_format, e.message), 400
-        else:
+    except Exception as e:
+        logger.exception('search error')
         return index_error(output_format, gettext('search error')), 500
 
     # results