# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1480631243 -3600
# Node ID cb64d3e04c11a436e3d4a3386ae3dc3e529527d7
# Parent  79c82d827bbe2cefa22606bfb682810ee8802731
Supported Sliceobj usage, introduced slice step information to __getslice__.
Added tests involving slices.

diff -r 79c82d827bbe -r cb64d3e04c11 lib/__builtins__/sequence.py
--- a/lib/__builtins__/sequence.py	Thu Dec 01 23:06:26 2016 +0100
+++ b/lib/__builtins__/sequence.py	Thu Dec 01 23:27:23 2016 +0100
@@ -49,7 +49,7 @@
         # Handle slices separately.
 
         elif _isinstance(index, slice):
-            return self.__getslice__(index.start, index.end)
+            return self.__getslice__(index.start, index.end, index.step)
 
         # No other kinds of objects are supported as indexes.
 
@@ -77,9 +77,16 @@
         else:
             raise TypeError()
 
-    def __getslice__(self, start, end=None):
+    def __getslice__(self, start, end=None, step=1):
 
-        "Return a slice starting from 'start', with the optional 'end'."
+        """
+        Return a slice of the sequence starting from the 'start' index, ending
+        before the optional 'end' (or at the end of the sequence), and providing
+        items at the frequency given by 'step' (with a default step of 1).
+        """
+
+        if step == 0:
+            raise ValueError(step)
 
         length = self.__len__()
 
@@ -101,9 +108,9 @@
 
         result = []
 
-        while start < end:
+        while step > 0 and start < end or step < 0 and start > end:
             result.append(self.__get_single_item__(start))
-            start += 1
+            start += step
 
         return result
 
diff -r 79c82d827bbe -r cb64d3e04c11 lib/operator/__init__.py
--- a/lib/operator/__init__.py	Thu Dec 01 23:06:26 2016 +0100
+++ b/lib/operator/__init__.py	Thu Dec 01 23:27:23 2016 +0100
@@ -80,4 +80,6 @@
     pos,
     )
 
+from __builtins__.span import slice # for Sliceobj instantiation
+
 # vim: tabstop=4 expandtab shiftwidth=4
diff -r 79c82d827bbe -r cb64d3e04c11 tests/slice.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/slice.py	Thu Dec 01 23:27:23 2016 +0100
@@ -0,0 +1,12 @@
+l = range(0, 10)
+print l                     # [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+
+s = slice(2, 5)
+print s                     # __builtins__.span.slice(2, 5, 1)
+
+print l[s]                  # [2, 3, 4]
+print l[2:5]                # [2, 3, 4]
+print l[2:5:-1]             # []
+print l[5:2:-1]             # [5, 4, 3]
+print l[1:9:2]              # [1, 3, 5, 7]
+print l[9:1:-2]             # [9, 7, 5, 3]