# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1480291181 -3600
# Node ID cc05fadb5fb43d1392612ac93c1992270cd5885d
# Parent  b22e901e12d6656632525814d76116acf3ee02e2
Introduced proper checking of negative indexes, simplifying index handling.

diff -r b22e901e12d6 -r cc05fadb5fb4 lib/__builtins__/list.py
--- a/lib/__builtins__/list.py	Mon Nov 28 00:53:13 2016 +0100
+++ b/lib/__builtins__/list.py	Mon Nov 28 00:59:41 2016 +0100
@@ -107,18 +107,14 @@
 
         "Return the item at the normalised (positive) 'index'."
 
-        if index >= len(self):
-            raise IndexError(index)
-
+        self._check_index(index)
         return native._list_element(self, index)
 
     def __set_single_item__(self, index, value):
 
         "Set at the normalised (positive) 'index' the given 'value'."
 
-        if index >= len(self):
-            raise IndexError(index)
-
+        self._check_index(index)
         return native._list_setelement(self, index, value)
 
 # vim: tabstop=4 expandtab shiftwidth=4
diff -r b22e901e12d6 -r cc05fadb5fb4 lib/__builtins__/sequence.py
--- a/lib/__builtins__/sequence.py	Mon Nov 28 00:53:13 2016 +0100
+++ b/lib/__builtins__/sequence.py	Mon Nov 28 00:59:41 2016 +0100
@@ -54,7 +54,7 @@
         # ones.
 
         if _isinstance(index, int):
-            index = _normalise_index(index, self.__len__())
+            index = _get_absolute_index(index, self.__len__())
             return self.__get_single_item__(index)
 
         # Handle slices separately.
@@ -75,7 +75,7 @@
         # ones.
 
         if _isinstance(index, int):
-            index = _normalise_index(index, self.__len__())
+            index = _get_absolute_index(index, self.__len__())
             return self.__set_single_item__(index, value)
 
         # Handle slices separately.
@@ -100,7 +100,7 @@
         if start is None:
             start = 0
         else:
-            start = _normalise_index(start, length)
+            start = _get_absolute_index(start, length)
 
         # Handle a null end as the first position after the end of the sequence,
         # otherwise normalising any end index.
@@ -108,7 +108,7 @@
         if end is None:
             end = length
         else:
-            end = _normalise_index(end, length)
+            end = _get_absolute_index(end, length)
 
         result = []
 
@@ -118,6 +118,16 @@
 
         return result
 
+    def _check_index(self, index):
+
+        """
+        Check the given absolute 'index', raising an IndexError if out of
+        bounds.
+        """
+
+        if index < 0 or index >= len(self):
+            raise IndexError(index)
+
 def _get_absolute_index(index, length):
 
     """
@@ -130,12 +140,6 @@
     else:
         return index
 
-def _normalise_index(index, length):
-
-    "Normalise 'index' for a collection having the specified 'length'."
-
-    return _min(length, _max(0, _get_absolute_index(index, length)))
-
 def _max(x, y):
 
     "Return the maximum of 'x' and 'y'."
diff -r b22e901e12d6 -r cc05fadb5fb4 lib/__builtins__/tuple.py
--- a/lib/__builtins__/tuple.py	Mon Nov 28 00:53:13 2016 +0100
+++ b/lib/__builtins__/tuple.py	Mon Nov 28 00:59:41 2016 +0100
@@ -86,9 +86,7 @@
 
         "Return the item at the normalised (positive) 'index'."
 
-        if index >= len(self):
-            raise IndexError(index)
-
+        self._check_index(index)
         return native._list_element(self, index)
 
     def __set_single_item__(self, index, value):