Refactor logging handling

Old system was using manual string formatting for log messages.
This caused issues with common operations like exception logging
because often they need to be handled differently for Py2/Py3
compatibility. In order to unify the effort:

 - All logging is changed to `logging.level(msg, arg1, arg2)` style.
 - A `SafeLogger` is implemented to auto-decode exceptions properly
in the args (ref #1403).
 - Custom formatters were overriding useful logging functionality
like traceback outputing (ref #1402). They are refactored to be
more transparent. Traceback information is provided in `--debug`
mode for `read_file` errors in generators.
 - Formatters will now auto-format multiline log messages in order
to make them look related. Similarly, traceback will be formatted in
the same fashion.
 - `pelican.log.LimitFilter` was (ab)using logging message which
would result in awkward syntax for argumented logging style. This
functionality is moved to `extra` keyword argument.
 - Levels for errors that would result skipping a file (`read_file`)
changed from `warning` to `error` in order to make them stand out
among other logs.
 - Small consistency changes to log messages (i.e. changing all
to start with an uppercase letter) and quality-of-life improvements
(some log messages were dumping raw object information).

pelican/__init__.py

@@ -70,16 +70,16 @@ class Pelican(object):
         for plugin in self.settings['PLUGINS']:
             # if it's a string, then import it
             if isinstance(plugin, six.string_types):
-                logger.debug("Loading plugin `{0}`".format(plugin))
+                logger.debug("Loading plugin `%s`", plugin)
                 try:
                     plugin = __import__(plugin, globals(), locals(),
                                         str('module'))
                 except ImportError as e:
                     logger.error(
-                        "Can't find plugin `{0}`: {1}".format(plugin, e))
+                        "Cannot load plugin `%s`\n%s", plugin, e)
                     continue
 
-            logger.debug("Registering plugin `{0}`".format(plugin.__name__))
+            logger.debug("Registering plugin `%s`", plugin.__name__)
             plugin.register()
             self.plugins.append(plugin)
         logger.debug('Restoring system path')
@@ -99,7 +99,7 @@ class Pelican(object):
 
             for setting in ('ARTICLE_URL', 'ARTICLE_LANG_URL', 'PAGE_URL',
                             'PAGE_LANG_URL'):
-                logger.warning("%s = '%s'" % (setting, self.settings[setting]))
+                logger.warning("%s = '%s'", setting, self.settings[setting])
 
         if self.settings.get('ARTICLE_PERMALINK_STRUCTURE', False):
             logger.warning('Found deprecated `ARTICLE_PERMALINK_STRUCTURE` in'
@@ -124,7 +124,7 @@ class Pelican(object):
                             'PAGE_SAVE_AS', 'PAGE_LANG_SAVE_AS'):
                 self.settings[setting] = os.path.join(structure,
                                                       self.settings[setting])
-                logger.warning("%s = '%s'" % (setting, self.settings[setting]))
+                logger.warning("%s = '%s'", setting, self.settings[setting])
 
         for new, old in [('FEED', 'FEED_ATOM'), ('TAG_FEED', 'TAG_FEED_ATOM'),
                          ('CATEGORY_FEED', 'CATEGORY_FEED_ATOM'),
@@ -203,7 +203,7 @@ class Pelican(object):
 
             for v in value:
                 if isinstance(v, type):
-                    logger.debug('Found generator: {0}'.format(v))
+                    logger.debug('Found generator: %s', v)
                     generators.append(v)
 
         return generators
@@ -217,11 +217,11 @@ class Pelican(object):
         else:
             writer = writers[0]
             if writers_found == 1:
-                logger.debug('Found writer: {}'.format(writer))
+                logger.debug('Found writer: %s', writer)
             else:
                 logger.warning(
-                    '{} writers found, using only first one: {}'.format(
-                    writers_found, writer))
+                    '%s writers found, using only first one: %s', 
+                    writers_found, writer)
             return writer(self.output_path, settings=self.settings)
 
 
@@ -308,6 +308,7 @@ def get_config(args):
         config['CACHE_PATH'] = args.cache_path
     if args.selected_paths:
         config['WRITE_SELECTED'] = args.selected_paths.split(',')
+    config['DEBUG'] = args.verbosity == logging.DEBUG
 
     # argparse returns bytes in Py2. There is no definite answer as to which
     # encoding argparse (or sys.argv) uses.
@@ -404,7 +405,7 @@ def main():
                         logger.critical(e.args)
                         raise
                     logger.warning(
-                        'Caught exception "{0}". Reloading.'.format(e))
+                        'Caught exception "%s". Reloading.', e)
 
                 finally:
                     time.sleep(.5)  # sleep to avoid cpu load
@@ -419,13 +420,7 @@ def main():
             pelican.run()
 
     except Exception as e:
-        # localized systems have errors in native language if locale is set
-        # so convert the message to unicode with the correct encoding
-        msg = str(e)
-        if not six.PY3:
-            msg = msg.decode(locale.getpreferredencoding())
-
-        logger.critical(msg)
+        logger.critical('%s', e)
 
         if args.verbosity == logging.DEBUG:
             raise