Improve extended slicing support in builtin types and classes. Specifically:

 - Specialcase extended slices that amount to a shallow copy the same way as
   is done for simple slices, in the tuple, string and unicode case.

 - Specialcase step-1 extended slices to optimize the common case for all
   involved types.

 - For lists, allow extended slice assignment of differing lengths as long
   as the step is 1. (Previously, 'l[:2:1] = []' failed even though
   'l[:2] = []' and 'l[:2:None] = []' do not.)

 - Implement extended slicing for buffer, array, structseq, mmap and
   UserString.UserString.

 - Implement slice-object support (but not non-step-1 slice assignment) for
   UserString.MutableString.

 - Add tests for all new functionality.

1 files changed, 12 insertions, 2 deletions

diff --git a/Lib/test/string_tests.py b/Lib/test/string_tests.py
index d38e4a98dd..d0f8c03c7e 100644
--- a/Lib/test/string_tests.py
+++ b/Lib/test/string_tests.py
@@ -912,7 +912,6 @@ class MixinStrUnicodeUserStringTest:
         self.checkequal(u'abc', 'abc', '__getitem__', slice(0, 1000))
         self.checkequal(u'a', 'abc', '__getitem__', slice(0, 1))
         self.checkequal(u'', 'abc', '__getitem__', slice(0, 0))
-        # FIXME What about negative indices? This is handled differently by [] and __getitem__(slice)
 
         self.checkraises(TypeError, 'abc', '__getitem__', 'def')
 
@@ -926,10 +925,21 @@ class MixinStrUnicodeUserStringTest:
         self.checkequal('', 'abc', '__getslice__', 1000, 1000)
         self.checkequal('', 'abc', '__getslice__', 2000, 1000)
         self.checkequal('', 'abc', '__getslice__', 2, 1)
-        # FIXME What about negative indizes? This is handled differently by [] and __getslice__
 
         self.checkraises(TypeError, 'abc', '__getslice__', 'def')
 
+    def test_extended_getslice(self):
+        # Test extended slicing by comparing with list slicing.
+        s = string.ascii_letters + string.digits
+        indices = (0, None, 1, 3, 41, -1, -2, -37)
+        for start in indices:
+            for stop in indices:
+                # Skip step 0 (invalid)
+                for step in indices[1:]:
+                    L = list(s)[start:stop:step]
+                    self.checkequal(u"".join(L), s, '__getitem__',
+                                    slice(start, stop, step))
+
     def test_mul(self):
         self.checkequal('', 'abc', '__mul__', -1)
         self.checkequal('', 'abc', '__mul__', 0)