Ensure None, NaN, and Infinity are sorted consistently

Internally, these may be translated to the same value, so they will be
output in the same order they were input, which could lead to suprise.

This commit ensures the order is always consistent.

1 files changed, 11 insertions, 1 deletions

diff --git a/natsort/utils.py b/natsort/utils.py
index b86225e..2a3745f 100644
--- a/natsort/utils.py
+++ b/natsort/utils.py
@@ -420,7 +420,17 @@ def parse_number_or_none_factory(
         val: Any, _nan_replace: float = nan_replace, _sep: StrOrBytes = sep
     ) -> BasicTuple:
         """Given a number, place it in a tuple with a leading null string."""
-        return _sep, (_nan_replace if val != val or val is None else val)
+        # Add a trailing string numbers equaling _nan_replace. This will make
+        # the ordering between None NaN, and the NaN replacement value...
+        # None comes first, then NaN, then the replacement value.
+        if val is None:
+            return _sep, _nan_replace, "1"
+        elif val != val:
+            return _sep, _nan_replace, "2"
+        elif val == _nan_replace:
+            return _sep, _nan_replace, "3"
+        else:
+            return _sep, val
 
     # Return the function, possibly wrapping in tuple if PATH is selected.
     if alg & ns.PATH and alg & ns.UNGROUPLETTERS and alg & ns.LOCALEALPHA: