Always use native strings as keys.

src/allmydata/test/test_log.py

@@ -9,7 +9,7 @@ from __future__ import absolute_import
 from __future__ import division
 from __future__ import print_function
 
-from future.utils import PY2
+from future.utils import PY2, native_str
 if PY2:
     from builtins import filter, map, zip, ascii, chr, hex, input, next, oct, open, pow, round, super, bytes, dict, list, object, range, str, max, min  # noqa: F401
 
@@ -154,3 +154,17 @@ class Log(unittest.TestCase):
         obj.log("four")
         self.assertEqual([m[2] for m in self.messages],
                          ["grand", "par1", "par2", "msg1", "msg1"])
+
+    def test_native_string_keys(self):
+        """Keyword argument keys are all native strings."""
+        class LoggingObject17(tahoe_log.PrefixingLogMixin):
+            pass
+
+        obj = LoggingObject17()
+        # Native string by default:
+        obj.log(hello="world")
+        # Will be Unicode on Python 2:
+        obj.log(**{"my": "message"})
+        for message in self.messages:
+            for k in message[-1].keys():
+                self.assertIsInstance(k, native_str)

src/allmydata/util/log.py

@@ -11,6 +11,7 @@ from __future__ import unicode_literals
 from future.utils import PY2
 if PY2:
     from builtins import filter, map, zip, ascii, chr, hex, input, next, oct, open, pow, round, super, bytes, dict, list, object, range, str, max, min  # noqa: F401
+from six import ensure_str
 
 from pyutil import nummedobj
 
@@ -55,6 +56,7 @@ class LogMixin(object):
             pmsgid = self._parentmsgid
             if pmsgid is None:
                 pmsgid = self._grandparentmsgid
+        kwargs = {ensure_str(k): v for (k, v) in kwargs.items()}
         msgid = log.msg(msg, facility=facility, parent=pmsgid, *args, **kwargs)
         if self._parentmsgid is None:
             self._parentmsgid = msgid