Offer new-style formatting for logging

beets.logging is a drop-in replacement for logging. Any logger created
from beets.logging.getLogger() will use {}-style formatting instead of
%-style, on python 2 and 3.

beets/logging.py

@@ -0,0 +1,37 @@
+"""Allow {}-style formatting on python 2 and 3
+
+Provide everything the "logging" module does, the only difference is that when
+getLogger(name) instantiates a logger that logger uses {}-style formatting.
+"""
+
+from __future__ import absolute_import
+from copy import copy
+from logging import *
+
+
+# create a str.format-based logger
+class StrFormatLogger(Logger):
+    class _LogMessage(object):
+        def __init__(self, msg, args, kwargs):
+            self.msg = msg
+            self.args = args
+            self.kwargs = kwargs
+
+        def __str__(self):
+            return self.msg.format(*self.args, **self.kwargs)
+
+    def _log(self, level, msg, args, exc_info=None, extra=None, **kwargs):
+        """Log 'msg.format(*args, **kwargs)"""
+        msg = self._LogMessage(msg, args, kwargs)
+        return super(StrFormatLogger, self)._log(level, msg, (), exc_info, extra)
+
+
+my_manager = copy(Logger.manager)
+my_manager.loggerClass = StrFormatLogger
+
+
+def getLogger(name=None):
+    if name:
+        return my_manager.getLogger(name)
+    else:
+        return root