# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1485727003 -3600
# Node ID b2b0c13d325228f54533a1aebc5f0a3fd4f3ebff
# Parent  c79b1be65ef255c53be0591b8b31e634ee4e9f59
Confine indexes used in slicing operations, returning empty sequences where
indexes specify regions outside the bounds of the provided sequences.
Handle quoting of quote characters before typically-unquoted characters.

diff -r c79b1be65ef2 -r b2b0c13d3252 lib/__builtins__/sequence.py
--- a/lib/__builtins__/sequence.py	Sun Jan 29 18:52:35 2017 +0100
+++ b/lib/__builtins__/sequence.py	Sun Jan 29 22:56:43 2017 +0100
@@ -3,7 +3,7 @@
 """
 Sequence operations.
 
-Copyright (C) 2015, 2016 Paul Boddie <paul@boddie.org.uk>
+Copyright (C) 2015, 2016, 2017 Paul Boddie <paul@boddie.org.uk>
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -36,15 +36,21 @@
         if index < 0 or index >= self.__len__():
             raise IndexError(index)
 
-    def _check_end_index(self, index):
+    def _confine_index(self, index):
 
         """
-        Check the given absolute end 'index', raising an IndexError if out of
-        bounds.
+        Return the given absolute 'index', confined by the bounds of the
+        sequence.
         """
 
-        if index < -1 or index > self.__len__():
-            raise IndexError(index)
+        length = self.__len__()
+
+        if index < 0:
+            return 0
+        elif index > length:
+            return length
+        else:
+            return index
 
     def __getitem__(self, index):
 
diff -r c79b1be65ef2 -r b2b0c13d3252 lib/__builtins__/str.py
--- a/lib/__builtins__/str.py	Sun Jan 29 18:52:35 2017 +0100
+++ b/lib/__builtins__/str.py	Sun Jan 29 22:56:43 2017 +0100
@@ -96,10 +96,20 @@
 
         while i < end:
             c = self[i]
-            n = ord(c)
+
+            # Handle quotes before anything else.
+
+            if c == quote:
+                b.append("\\")
+                b.append(quote)
+                i += 1
+                last = i
+                continue
 
             # Extended unquoted text.
 
+            n = ord(c)
+
             if 32 <= n < 128:
                 i += 1
                 continue
@@ -110,10 +120,7 @@
 
             # Add quoted value.
 
-            if c == quote:
-                b.append("\\")
-                b.append(quote)
-            elif c == "\t":
+            if c == "\t":
                 b.append("\\t")
             elif c == "\n":
                 b.append("\\n")
@@ -530,8 +537,8 @@
         intervals.
         """
 
-        self._check_index(start)
-        self._check_end_index(end)
+        start = self._confine_index(start)
+        end = self._confine_index(end)
         check_int(step)
 
         if step == 0:
diff -r c79b1be65ef2 -r b2b0c13d3252 lib/__builtins__/unicode.py
--- a/lib/__builtins__/unicode.py	Sun Jan 29 18:52:35 2017 +0100
+++ b/lib/__builtins__/unicode.py	Sun Jan 29 22:56:43 2017 +0100
@@ -3,7 +3,7 @@
 """
 Unicode objects.
 
-Copyright (C) 2015, 2016 Paul Boddie <paul@boddie.org.uk>
+Copyright (C) 2015, 2016, 2017 Paul Boddie <paul@boddie.org.uk>
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -179,8 +179,8 @@
         intervals.
         """
 
-        self._check_index(start)
-        self._check_end_index(end)
+        start = self._confine_index(start)
+        end = self._confine_index(end)
         check_int(step)
 
         if step == 0:
diff -r c79b1be65ef2 -r b2b0c13d3252 tests/string.py
--- a/tests/string.py	Sun Jan 29 18:52:35 2017 +0100
+++ b/tests/string.py	Sun Jan 29 22:56:43 2017 +0100
@@ -6,6 +6,10 @@
 print s[5:]                 #  world!
 print s[1:10:2]             # el ol
 print s[10:1:-2]            # drwol
+print s[11:]                # !
+print s[:-11]               # H
+print s[12:]                #
+print s[:-12]               #
 print s.find("w")           # 6
 print s.find("w", 7)        # -1
 print s.find("w", 0, 6)     # -1