Support logging.propagate to avoid duplicate log entries.

- Resolves Issue #310

CHANGELOG.md

@@ -4,7 +4,8 @@
 
 Bugs: 
 
-- None
+- `[ext.logging]` Support `logging.propagate` to avoid duplicate log entries.
+    - [Issue #310](https://github.com/datafolklabs/cement/issues/310)
 
 
 Features:

cement/ext/ext_logging.py

@@ -93,6 +93,18 @@ class LoggingLogHandler(log.LogHandler):
         #: The help description for the log level argument
         log_level_argument_help = 'logging level'
 
+        #: Whether or not to propagate logs up to parents. Likely should
+        #: always be ``False``, but is here in the off chance this breaks
+        #: something. Setting to ``False`` resolves situation where duplicate
+        #: logs appears when using other libraries who logged to the root
+        #: logger.
+        #:
+        #: Note, if attempting to use PyTest ``caplog`` fixture, this may need
+        #: to be set to ``True``.
+        #:
+        #: See: ``tests.ext.test_ext_colorlog.test_colorlog``.
+        propagate = False
+
     levels = ['INFO', 'WARNING', 'ERROR', 'DEBUG', 'FATAL', 'CRITICAL']
 
     def __init__(self, *args, **kw):
@@ -113,6 +125,7 @@ class LoggingLogHandler(log.LogHandler):
 
         level = self.app.config.get(self._meta.config_section, 'level')
         self.set_level(level)
+        self.backend.propagate = self._meta.propagate
 
         LOG.debug("logging initialized for '%s' using %s" %
                   (self._meta.namespace, self.__class__.__name__))
@@ -158,6 +171,10 @@ class LoggingLogHandler(log.LogHandler):
     def clear_loggers(self, namespace):
         """Clear any previously configured loggers for ``namespace``."""
 
+        # clear root loggers
+        # logging.getLogger().handlers = []
+        # logging.l
+
         for i in logging.getLogger("cement:app:%s" % namespace).handlers:
             logging.getLogger("cement:app:%s" % namespace).removeHandler(i)
 

tests/ext/test_ext_colorlog.py

@@ -22,7 +22,9 @@ class ColorlogApp(TestApp):
 
 
 def test_colorlog(caplog):
-    with ColorlogApp() as app:
+    META = init_defaults('log.colorlog')
+    META['log.colorlog']['propagate'] = True
+    with ColorlogApp(meta_defaults=META) as app:
         app.run()
         app.log.info('this is an info message')
         app.log.warning('this is a warning message')