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.

Lib/UserString.py

@@ -149,15 +149,41 @@ def __init__(self, string=""):
     def __hash__(self):
         raise TypeError, "unhashable type (it is mutable)"
     def __setitem__(self, index, sub):
-        if index < 0:
-            index += len(self.data)
-        if index < 0 or index >= len(self.data): raise IndexError
-        self.data = self.data[:index] + sub + self.data[index+1:]
+        if isinstance(index, slice):
+            if isinstance(sub, UserString):
+                sub = sub.data
+            elif not isinstance(sub, basestring):
+                sub = str(sub)
+            start, stop, step = index.indices(len(self.data))
+            if step == -1:
+                start, stop = stop+1, start+1
+                sub = sub[::-1]
+            elif step != 1:
+                # XXX(twouters): I guess we should be reimplementing
+                # the extended slice assignment/deletion algorithm here...
+                raise TypeError, "invalid step in slicing assignment"
+            start = min(start, stop)
+            self.data = self.data[:start] + sub + self.data[stop:]
+        else:
+            if index < 0:
+                index += len(self.data)
+            if index < 0 or index >= len(self.data): raise IndexError
+            self.data = self.data[:index] + sub + self.data[index+1:]
     def __delitem__(self, index):
-        if index < 0:
-            index += len(self.data)
-        if index < 0 or index >= len(self.data): raise IndexError
-        self.data = self.data[:index] + self.data[index+1:]
+        if isinstance(index, slice):
+            start, stop, step = index.indices(len(self.data))
+            if step == -1:
+                start, stop = stop+1, start+1
+            elif step != 1:
+                # XXX(twouters): see same block in __setitem__
+                raise TypeError, "invalid step in slicing deletion"
+            start = min(start, stop)
+            self.data = self.data[:start] + self.data[stop:]
+        else:
+            if index < 0:
+                index += len(self.data)
+            if index < 0 or index >= len(self.data): raise IndexError
+            self.data = self.data[:index] + self.data[index+1:]
     def __setslice__(self, start, end, sub):
         start = max(start, 0); end = max(end, 0)
         if isinstance(sub, UserString):

Lib/test/list_tests.py

@@ -179,8 +179,10 @@ def test_setslice(self):
         self.assertEqual(a, self.type2test(range(10)))
 
         self.assertRaises(TypeError, a.__setslice__, 0, 1, 5)
+        self.assertRaises(TypeError, a.__setitem__, slice(0, 1, 5))
 
         self.assertRaises(TypeError, a.__setslice__)
+        self.assertRaises(TypeError, a.__setitem__)
 
     def test_delslice(self):
         a = self.type2test([0, 1])

Lib/test/string_tests.py

@@ -912,7 +912,6 @@ def test_subscript(self):
         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 @@ def test_slice(self):
         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)

Lib/test/test_array.py

@@ -474,6 +474,18 @@ def test_getslice(self):
             array.array(self.typecode)
         )
 
+    def test_extended_getslice(self):
+        # Test extended slicing by comparing with list slicing
+        # (Assumes list conversion works correctly, too)
+        a = array.array(self.typecode, self.example)
+        indices = (0, None, 1, 3, 19, 100, -1, -2, -31, -100)
+        for start in indices:
+            for stop in indices:
+                # Everything except the initial 0 (invalid step)
+                for step in indices[1:]:
+                    self.assertEqual(list(a[start:stop:step]),
+                                     list(a)[start:stop:step])
+
     def test_setslice(self):
         a = array.array(self.typecode, self.example)
         a[:1] = a
@@ -557,12 +569,34 @@ def test_setslice(self):
 
         a = array.array(self.typecode, self.example)
         self.assertRaises(TypeError, a.__setslice__, 0, 0, None)
+        self.assertRaises(TypeError, a.__setitem__, slice(0, 0), None)
         self.assertRaises(TypeError, a.__setitem__, slice(0, 1), None)
 
         b = array.array(self.badtypecode())
         self.assertRaises(TypeError, a.__setslice__, 0, 0, b)
+        self.assertRaises(TypeError, a.__setitem__, slice(0, 0), b)
         self.assertRaises(TypeError, a.__setitem__, slice(0, 1), b)
 
+    def test_extended_set_del_slice(self):
+        indices = (0, None, 1, 3, 19, 100, -1, -2, -31, -100)
+        for start in indices:
+            for stop in indices:
+                # Everything except the initial 0 (invalid step)
+                for step in indices[1:]:
+                    a = array.array(self.typecode, self.example)
+                    L = list(a)
+                    # Make sure we have a slice of exactly the right length,
+                    # but with (hopefully) different data.
+                    data = L[start:stop:step]
+                    data.reverse()
+                    L[start:stop:step] = data
+                    a[start:stop:step] = array.array(self.typecode, data)
+                    self.assertEquals(a, array.array(self.typecode, L))
+
+                    del L[start:stop:step]
+                    del a[start:stop:step]
+                    self.assertEquals(a, array.array(self.typecode, L))
+
     def test_index(self):
         example = 2*self.example
         a = array.array(self.typecode, example)

Lib/test/test_buffer.py

@@ -0,0 +1,29 @@
+"""Unit tests for buffer objects.
+
+For now, tests just new or changed functionality.
+
+"""
+
+import unittest
+from test import test_support
+
+class BufferTests(unittest.TestCase):
+
+    def test_extended_getslice(self):
+        # Test extended slicing by comparing with list slicing.
+        s = "".join(chr(c) for c in list(range(255, -1, -1)))
+        b = buffer(s)
+        indices = (0, None, 1, 3, 19, 300, -1, -2, -31, -300)
+        for start in indices:
+            for stop in indices:
+                # Skip step 0 (invalid)
+                for step in indices[1:]:
+                    self.assertEqual(b[start:stop:step],
+                                     s[start:stop:step])
+
+
+def test_main():
+    test_support.run_unittest(BufferTests)
+
+if __name__ == "__main__":
+    test_main()

Lib/test/test_mmap.py

@@ -306,6 +306,40 @@ def test_anonymous(self):
             m[x] = ch = chr(x & 255)
             self.assertEqual(m[x], ch)
 
+    def test_extended_getslice(self):
+        # Test extended slicing by comparing with list slicing.
+        s = "".join(chr(c) for c in reversed(range(256)))
+        m = mmap.mmap(-1, len(s))
+        m[:] = s
+        self.assertEqual(m[:], s)
+        indices = (0, None, 1, 3, 19, 300, -1, -2, -31, -300)
+        for start in indices:
+            for stop in indices:
+                # Skip step 0 (invalid)
+                for step in indices[1:]:
+                    self.assertEqual(m[start:stop:step],
+                                     s[start:stop:step])
+
+    def test_extended_set_del_slice(self):
+        # Test extended slicing by comparing with list slicing.
+        s = "".join(chr(c) for c in reversed(range(256)))
+        m = mmap.mmap(-1, len(s))
+        indices = (0, None, 1, 3, 19, 300, -1, -2, -31, -300)
+        for start in indices:
+            for stop in indices:
+                # Skip invalid step 0
+                for step in indices[1:]:
+                    m[:] = s
+                    self.assertEqual(m[:], s)
+                    L = list(s)
+                    # Make sure we have a slice of exactly the right length,
+                    # but with different data.
+                    data = L[start:stop:step]
+                    data = "".join(reversed(data))
+                    L[start:stop:step] = data
+                    m[start:stop:step] = data
+                    self.assertEquals(m[:], "".join(L))
+
 def test_main():
     run_unittest(MmapTests)
 

Lib/test/test_structseq.py

@@ -97,6 +97,18 @@ def test_reduce(self):
         t = time.gmtime()
         x = t.__reduce__()
 
+    def test_extended_getslice(self):
+        # Test extended slicing by comparing with list slicing.
+        t = time.gmtime()
+        L = list(t)
+        indices = (0, None, 1, 3, 19, 300, -1, -2, -31, -300)
+        for start in indices:
+            for stop in indices:
+                # Skip step 0 (invalid)
+                for step in indices[1:]:
+                    self.assertEqual(list(t[start:stop:step]),
+                                     L[start:stop:step])
+
 def test_main():
     test_support.run_unittest(StructSeqTest)
 

Lib/test/test_userstring.py

@@ -3,6 +3,7 @@
 # UserString instances should behave similar to builtin string objects.
 
 import unittest
+import string
 from test import test_support, string_tests
 
 from UserString import UserString, MutableString
@@ -88,6 +89,28 @@ def test_delslice(self):
         del s[-1:10]
         self.assertEqual(s, "fo")
 
+    def test_extended_set_del_slice(self):
+        indices = (0, None, 1, 3, 19, 100, -1, -2, -31, -100)
+        orig = string.ascii_letters + string.digits
+        for start in indices:
+            for stop in indices:
+                # Use indices[1:] when MutableString can handle real
+                # extended slices
+                for step in (None, 1, -1):
+                    s = self.type2test(orig)
+                    L = list(orig)
+                    # Make sure we have a slice of exactly the right length,
+                    # but with (hopefully) different data.
+                    data = L[start:stop:step]
+                    data.reverse()
+                    L[start:stop:step] = data
+                    s[start:stop:step] = "".join(data)
+                    self.assertEquals(s, "".join(L))
+
+                    del L[start:stop:step]
+                    del s[start:stop:step]
+                    self.assertEquals(s, "".join(L))
+
     def test_immutable(self):
         s = self.type2test("foobar")
         s2 = s.immutable()