Another function that should be a no-op on Python 3.

src/allmydata/test/test_encodingutil.py

@@ -144,6 +144,7 @@ class EncodingUtilErrors(ReallyEqualMixin, unittest.TestCase):
                               argv_to_unicode,
                               lumiere_nfc.encode('latin1'))
 
+    @skipIf(PY3, "Python 2 only.")
     def test_unicode_to_output(self):
         encodingutil.io_encoding = 'koi8-r'
         self.failUnlessRaises(UnicodeEncodeError, unicode_to_output, lumiere_nfc)
@@ -228,7 +229,8 @@ class EncodingUtil(ReallyEqualMixin):
     def test_unicode_to_url(self):
         self.failUnless(unicode_to_url(lumiere_nfc), b"lumi\xc3\xa8re")
 
-    def test_unicode_to_output(self):
+    @skipIf(PY3, "Python 3 is always Unicode, regardless of OS.")
+    def test_unicode_to_output_py2(self):
         if 'argv' not in dir(self):
             return
 
@@ -239,6 +241,10 @@ class EncodingUtil(ReallyEqualMixin):
         _reload()
         self.failUnlessReallyEqual(unicode_to_output(lumiere_nfc), self.argv)
 
+    @skipIf(PY2, "Python 3 only.")
+    def test_unicode_to_output_py3(self):
+        self.failUnlessReallyEqual(unicode_to_output(lumiere_nfc), lumiere_nfc)
+
     @skipIf(PY3, "Python 2 only.")
     def test_unicode_to_argv_py2(self):
         """unicode_to_argv() converts to bytes on Python 2."""

src/allmydata/util/encodingutil.py

@@ -21,6 +21,7 @@ from past.builtins import unicode
 
 import sys, os, re, locale
 import unicodedata
+import warnings
 
 from allmydata.util.assertutil import precondition, _assert
 from twisted.python import usage
@@ -140,6 +141,8 @@ def unicode_to_argv(s, mangle=False):
     """
     precondition(isinstance(s, unicode), s)
     if PY3:
+        warnings.warn("This will be unnecessary once Python 2 is dropped.",
+                      DeprecationWarning)
         return s
 
     if mangle and sys.platform == "win32":
@@ -185,6 +188,10 @@ def unicode_to_output(s):
     Encode an unicode object for representation on stdout or stderr.
     """
     precondition(isinstance(s, unicode), s)
+    if PY3:
+        warnings.warn("This will be unnecessary once Python 2 is dropped.",
+                      DeprecationWarning)
+        return s
 
     try:
         out = s.encode(io_encoding)