Fix "always last" separator for Python 2.

The implementation that was used for the "always last" separator
for NUMAFTER when LOCALE was turned on for non-OSX OSs was buggy.

This new implementation does not rely on string value tricks, but rather
implements a sentinel-based methodology to identify the "always last"
separator and place it last explicitly.

1 files changed, 22 insertions, 12 deletions

diff --git a/natsort/compat/locale.py b/natsort/compat/locale.py
index a1cfa5a..cc386a2 100644
--- a/natsort/compat/locale.py
+++ b/natsort/compat/locale.py
@@ -14,7 +14,6 @@ from natsort.compat.py23 import (
     PY_VERSION,
     cmp_to_key,
     py23_unichr,
-    py23_cmp,
 )
 
 # This string should be sorted after any other byte string because
@@ -62,20 +61,31 @@ except ImportError:
     import locale
     if PY_VERSION < 3:
         from locale import strcoll
-        strxfrm = cmp_to_key(strcoll)
+        sentinel = object()
+
+        def custom_strcoll(a, b, last=sentinel):
+            """strcoll that can handle a sentinel that is always last."""
+            if a is last:
+                if b is last:
+                    return 0
+                else:
+                    return 1
+            elif b is last:  # a cannot also be sentinel b/c above logic
+                return -1
+            else:  # neither are sentinel
+                return strcoll(a, b)
+
+        strxfrm = cmp_to_key(custom_strcoll)
+        null_string_locale = strxfrm('')
+        null_string_locale_max = strxfrm(sentinel)
     else:
         from locale import strxfrm
+        null_string_locale = ''
 
-    null_string_locale = ''
-
-    # This string should be sorted after any other byte string because
-    # it contains the max unicode character repeated 20 times.
-    # You would need some odd data to come after that.
-    null_string_locale_max = py23_unichr(sys.maxunicode) * 20
-
-    if PY_VERSION < 3:
-        null_string_locale = cmp_to_key(py23_cmp)(null_string_locale)
-        null_string_locale_max = cmp_to_key(py23_cmp)(null_string_locale_max)
+        # This string should be sorted after any other byte string because
+        # it contains the max unicode character repeated 20 times.
+        # You would need some odd data to come after that.
+        null_string_locale_max = py23_unichr(sys.maxunicode) * 20
 
     # On some systems, locale is broken and does not sort in the expected
     # order. We will try to detect this and compensate.