Resurrected support for byte strings as list values

Signed-off-by: Andreas Maier <andreas.r.maier@gmx.de>

README.rst

@@ -47,13 +47,15 @@ methods added in Python 3.3 to the built-in ``list`` class.
 .. _list class of Python 3.8: https://docs.python.org/3.8/library/stdtypes.html#list
 .. _NocaseList: https://nocaselist.readthedocs.io/en/stable/reference.html#nocaselist.NocaseList
 
-The case-insensitivity is achieved by matching any list values as their
+The case-insensitivity is achieved by matching any key values as their
 casefolded values. By default, the casefolding is performed with
-`str.casefold()`_ on Python 3 and with `str.lower()`_ on Python 2.
+`str.casefold()`_ for unicode string keys and with `bytes.lower()`_ for byte
+string keys.
 The default casefolding can be overridden with a user-defined casefold method.
 
 .. _str.casefold(): https://docs.python.org/3/library/stdtypes.html#str.casefold
-.. _str.lower(): https://docs.python.org/2/library/stdtypes.html#str.lower
+.. _bytes.lower(): https://docs.python.org/3/library/stdtypes.html#bytes.lower
+
 
 Installation
 ------------

docs/changes.rst

@@ -20,6 +20,10 @@ Released: not yet
 
 **Enhancements:**
 
+* Resurrected support for byte strings as list values in the default
+  implementation of the casefold method. The list can now contains unicode
+  strings and byte strings.
+
 **Cleanup:**
 
 **Known issues:**

docs/intro.rst

@@ -36,7 +36,12 @@ for being case-insensitive, of course). This includes the ``clear()`` and
 
 The case-insensitivity is achieved by matching any key values as their
 casefolded values. By default, the casefolding is performed with
-:meth:`py:str.casefold` on Python 3 and with :meth:`py2:str.lower` on Python 2.
+:meth:`py:str.casefold` for unicode string keys and with :meth:`py:bytes.lower`
+for byte string keys.
+
+The :meth:`py:str.casefold` method implements the casefolding
+algorithm described in :term:`Default Case Folding in The Unicode Standard`.
+
 The default casefolding can be overridden with a user-defined casefold method.
 
 

nocaselist/_nocaselist.py

@@ -6,7 +6,6 @@
 
 import sys
 import os
-import six
 
 __all__ = ['NocaseList']
 
@@ -114,27 +113,28 @@ def __casefold__(value):
         It returns a case-insensitive form of the input value by calling a
         "casefold method" on the value. The input value will not be `None`.
 
-        The casefold method called by this method is :meth:`py:str.casefold`
-        on Python 3 and :meth:`py2:str.lower` on Python 2.
+        The casefold method called by this method is :meth:`py2:str.lower` on
+        Python 2, and on Python 3 it is :meth:`py:str.casefold`, falling back
+        to :meth:`py:bytes.lower` if it does not exist.
 
         This method can be overridden by users in order to change the
         case-insensitive behavior of the class.
         See :ref:`Overriding the default casefold method` for details.
 
         Parameters:
-          value (str or unicode): Input value, as a unicode string or in
-            Python 2 also as a byte string. Will not be `None`.
+          value (str or unicode or bytes): Input value. Will not be `None`.
 
         Returns:
-          str or unicode: Case-insensitive form of the input value, as a
-          unicode string or in Python 2 also as a byte string.
+          str or unicode or bytes: Case-insensitive form of the input value.
 
         Raises:
           AttributeError: The value does not have the casefold method.
         """
-        if six.PY2:
+        try:
+            return value.casefold()
+        except AttributeError:
+            # Either Python 2, or Python 3 and a byte string key
             return value.lower()
-        return value.casefold()
 
     def __getstate__(self):
         """