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 @@ class MutableString(UserString):
     def __hash__(self):
         raise TypeError, "unhashable type (it is mutable)"
     def __setitem__(self, index, sub):
-        if index < 0:
+        if isinstance(index, slice):
-            index += len(self.data)
+            if isinstance(sub, UserString):
-        if index < 0 or index >= len(self.data): raise IndexError
+                sub = sub.data
-        self.data = self.data[:index] + sub + self.data[index+1:]
+            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:
+        if isinstance(index, slice):
-            index += len(self.data)
+            start, stop, step = index.indices(len(self.data))
-        if index < 0 or index >= len(self.data): raise IndexError
+            if step == -1:
-        self.data = self.data[:index] + self.data[index+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 @@ class CommonTest(seq_tests.CommonTest):
         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 @@ 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)

Lib/test/test_array.py

@@ -474,6 +474,18 @@ class BaseTest(unittest.TestCase):
             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 @@ class BaseTest(unittest.TestCase):
 
         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 @@ class MmapTests(unittest.TestCase):
             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 @@ class StructSeqTest(unittest.TestCase):
         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 @@ class MutableStringTest(UserStringTest):
         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()

Modules/arraymodule.c

@@ -1605,6 +1605,16 @@ array_subscr(arrayobject* self, PyObject* item)
 		if (slicelength <= 0) {
 			return newarrayobject(&Arraytype, 0, self->ob_descr);
 		}
+		else if (step == 1) {
+			PyObject *result = newarrayobject(&Arraytype,
+						slicelength, self->ob_descr);
+			if (result == NULL)
+				return NULL;
+			memcpy(((arrayobject *)result)->ob_item,
+			       self->ob_item + start * itemsize,
+			       slicelength * itemsize);
+			return result;
+		}
 		else {
 			result = newarrayobject(&Arraytype, slicelength, self->ob_descr);
 			if (!result) return NULL;
@@ -1623,7 +1633,7 @@ array_subscr(arrayobject* self, PyObject* item)
 	}
 	else {
 		PyErr_SetString(PyExc_TypeError, 
-				"list indices must be integers");
+				"array indices must be integers");
 		return NULL;
 	}
 }
@@ -1631,112 +1641,146 @@ array_subscr(arrayobject* self, PyObject* item)
 static int
 array_ass_subscr(arrayobject* self, PyObject* item, PyObject* value)
 {
+	Py_ssize_t start, stop, step, slicelength, needed;
+	arrayobject* other;
+	int itemsize;
+
 	if (PyIndex_Check(item)) {
 		Py_ssize_t i = PyNumber_AsSsize_t(item, PyExc_IndexError);
-		if (i==-1 && PyErr_Occurred()) 
+		
+		if (i == -1 && PyErr_Occurred())
 			return -1;
 		if (i < 0)
 			i += Py_Size(self);
-		return array_ass_item(self, i, value);
+		if (i < 0 || i >= Py_Size(self)) {
-	}
+			PyErr_SetString(PyExc_IndexError,
-	else if (PySlice_Check(item)) {
+				"array assignment index out of range");
-		Py_ssize_t start, stop, step, slicelength;
-		int itemsize = self->ob_descr->itemsize;
-
-		if (PySlice_GetIndicesEx((PySliceObject*)item, Py_Size(self),
-				 &start, &stop, &step, &slicelength) < 0) {
 			return -1;
 		}
-
-		/* treat A[slice(a,b)] = v _exactly_ like A[a:b] = v */
-		if (step == 1 && ((PySliceObject*)item)->step == Py_None)
-			return array_ass_slice(self, start, stop, value);
-
 		if (value == NULL) {
-			/* delete slice */
+			/* Fall through to slice assignment */
-			Py_ssize_t cur, i, extra;
+			start = i;
-			
+			stop = i + 1;
-			if (slicelength <= 0)
+			step = 1;
-				return 0;
+			slicelength = 1;
-
-			if (step < 0) {
-				stop = start + 1;
-				start = stop + step*(slicelength - 1) - 1;
-				step = -step;
-			}
-
-			for (cur = start, i = 0; i < slicelength - 1;
-			     cur += step, i++) {
-				memmove(self->ob_item + (cur - i)*itemsize,
-					self->ob_item + (cur + 1)*itemsize,
-					(step - 1) * itemsize);
-			}
-			extra = Py_Size(self) - (cur + 1);
-			if (extra > 0) {
-				memmove(self->ob_item + (cur - i)*itemsize,
-					self->ob_item + (cur + 1)*itemsize,
-					extra*itemsize);
-			}
-
-			Py_Size(self) -= slicelength;
-			self->ob_item = (char *)PyMem_REALLOC(self->ob_item,
-							      itemsize*Py_Size(self));
-			self->allocated = Py_Size(self);
-
-			return 0;
 		}
-		else {
+		else
-			/* assign slice */
+			return (*self->ob_descr->setitem)(self, i, value);
-			Py_ssize_t cur, i;
+	}
-			arrayobject* av;
+	else if (PySlice_Check(item)) {
-
+		if (PySlice_GetIndicesEx((PySliceObject *)item,
-			if (!array_Check(value)) {
+					 Py_Size(self), &start, &stop,
-				PyErr_Format(PyExc_TypeError,
+					 &step, &slicelength) < 0) {
-			     "must assign array (not \"%.200s\") to slice",
+			return -1;
-					     Py_Type(value)->tp_name);
-				return -1;
-			}
-
-			av = (arrayobject*)value;
-
-			if (Py_Size(av) != slicelength) {
-				PyErr_Format(PyExc_ValueError,
-            "attempt to assign array of size %ld to extended slice of size %ld",
-					     /*XXX*/(long)Py_Size(av), /*XXX*/(long)slicelength);
-				return -1;
-			}
-
-			if (!slicelength)
-				return 0;
-
-			/* protect against a[::-1] = a */
-			if (self == av) { 
-				value = array_slice(av, 0, Py_Size(av));
-				av = (arrayobject*)value;
-				if (!av)
-					return -1;
-			} 
-			else {
-				Py_INCREF(value);
-			}
-
-			for (cur = start, i = 0; i < slicelength; 
-			     cur += step, i++) {
-				memcpy(self->ob_item + cur*itemsize,
-				       av->ob_item + i*itemsize,
-				       itemsize);
-			}
-
-			Py_DECREF(value);
-			
-			return 0;
 		}
-	} 
+	}
 	else {
-		PyErr_SetString(PyExc_TypeError, 
+		PyErr_SetString(PyExc_TypeError,
-				"list indices must be integers");
+				"array indices must be integer");
 		return -1;
 	}
+	if (value == NULL) {
+		other = NULL;
+		needed = 0;
+	}
+	else if (array_Check(value)) {
+		other = (arrayobject *)value;
+		needed = Py_Size(other);
+		if (self == other) {
+			/* Special case "self[i:j] = self" -- copy self first */
+			int ret;
+			value = array_slice(other, 0, needed);
+			if (value == NULL)
+				return -1;
+			ret = array_ass_subscr(self, item, value);
+			Py_DECREF(value);
+			return ret;
+		}
+		if (other->ob_descr != self->ob_descr) {
+			PyErr_BadArgument();
+			return -1;
+		}
+	}
+	else {
+		PyErr_Format(PyExc_TypeError,
+	     "can only assign array (not \"%.200s\") to array slice",
+			     Py_Type(value)->tp_name);
+		return -1;
+	}
+	itemsize = self->ob_descr->itemsize;
+	/* for 'a[2:1] = ...', the insertion point is 'start', not 'stop' */
+	if ((step > 0 && stop < start) ||
+	    (step < 0 && stop > start))
+		stop = start;
+	if (step == 1) {
+		if (slicelength > needed) {
+			memmove(self->ob_item + (start + needed) * itemsize,
+				self->ob_item + stop * itemsize,
+				(Py_Size(self) - stop) * itemsize);
+			if (array_resize(self, Py_Size(self) +
+					 needed - slicelength) < 0)
+				return -1;
+		}
+		else if (slicelength < needed) {
+			if (array_resize(self, Py_Size(self) +
+					 needed - slicelength) < 0)
+				return -1;
+			memmove(self->ob_item + (start + needed) * itemsize,
+				self->ob_item + stop * itemsize,
+				(Py_Size(self) - start - needed) * itemsize);
+		}
+		if (needed > 0)
+			memcpy(self->ob_item + start * itemsize,
+			       other->ob_item, needed * itemsize);
+		return 0;
+	}
+	else if (needed == 0) {
+		/* Delete slice */
+		Py_ssize_t cur, i;
+		
+		if (step < 0) {
+			stop = start + 1;
+			start = stop + step * (slicelength - 1) - 1;
+			step = -step;
+		}
+		for (cur = start, i = 0; i < slicelength;
+		     cur += step, i++) {
+			Py_ssize_t lim = step - 1;
+
+			if (cur + step >= Py_Size(self))
+				lim = Py_Size(self) - cur - 1;
+			memmove(self->ob_item + (cur - i) * itemsize,
+				self->ob_item + (cur + 1) * itemsize,
+				lim * itemsize);
+		}
+		cur = start + slicelength * step;
+		if (cur < Py_Size(self)) {
+			memmove(self->ob_item + (cur-slicelength) * itemsize,
+				self->ob_item + cur * itemsize,
+				(Py_Size(self) - cur) * itemsize);
+		}
+		if (array_resize(self, Py_Size(self) - slicelength) < 0)
+			return -1;
+		return 0;
+	}
+	else {
+		Py_ssize_t cur, i;
+
+		if (needed != slicelength) {
+			PyErr_Format(PyExc_ValueError,
+				"attempt to assign array of size %zd "
+				"to extended slice of size %zd",
+				needed, slicelength);
+			return -1;
+		}
+		for (cur = start, i = 0; i < slicelength;
+		     cur += step, i++) {
+			memcpy(self->ob_item + cur * itemsize,
+			       other->ob_item + i * itemsize,
+			       itemsize);
+		}
+		return 0;
+	}
 }
 
 static PyMappingMethods array_as_mapping = {

Modules/mmapmodule.c

@@ -680,6 +680,60 @@ mmap_slice(mmap_object *self, Py_ssize_t ilow, Py_ssize_t ihigh)
 	return PyString_FromStringAndSize(self->data + ilow, ihigh-ilow);
 }
 
+static PyObject *
+mmap_subscript(mmap_object *self, PyObject *item)
+{
+	CHECK_VALID(NULL);
+	if (PyIndex_Check(item)) {
+		Py_ssize_t i = PyNumber_AsSsize_t(item, PyExc_IndexError);
+		if (i == -1 && PyErr_Occurred())
+			return NULL;
+		if (i < 0)
+			i += self->size;
+		if (i < 0 || i > self->size) {
+			PyErr_SetString(PyExc_IndexError,
+				"mmap index out of range");
+			return NULL;
+		}
+		return PyString_FromStringAndSize(self->data + i, 1);
+	}
+	else if (PySlice_Check(item)) {
+		Py_ssize_t start, stop, step, slicelen;
+
+		if (PySlice_GetIndicesEx((PySliceObject *)item, self->size,
+				 &start, &stop, &step, &slicelen) < 0) {
+			return NULL;
+		}
+		
+		if (slicelen <= 0)
+			return PyString_FromStringAndSize("", 0);
+		else if (step == 1)
+			return PyString_FromStringAndSize(self->data + start,
+							  slicelen);
+		else {
+			char *result_buf = (char *)PyMem_Malloc(slicelen);
+			Py_ssize_t cur, i;
+			PyObject *result;
+
+			if (result_buf == NULL)
+				return PyErr_NoMemory();
+			for (cur = start, i = 0; i < slicelen;
+			     cur += step, i++) {
+			     	result_buf[i] = self->data[cur];
+			}
+			result = PyString_FromStringAndSize(result_buf,
+							    slicelen);
+			PyMem_Free(result_buf);
+			return result;
+		}
+	}
+	else {
+		PyErr_SetString(PyExc_TypeError,
+				"mmap indices must be integers");
+		return NULL;
+	}
+}
+
 static PyObject *
 mmap_concat(mmap_object *self, PyObject *bb)
 {
@@ -764,6 +818,96 @@ mmap_ass_item(mmap_object *self, Py_ssize_t i, PyObject *v)
 	return 0;
 }
 
+static int
+mmap_ass_subscript(mmap_object *self, PyObject *item, PyObject *value)
+{
+	CHECK_VALID(-1);
+
+	if (PyIndex_Check(item)) {
+		Py_ssize_t i = PyNumber_AsSsize_t(item, PyExc_IndexError);
+		const char *buf;
+
+		if (i == -1 && PyErr_Occurred())
+			return -1;
+		if (i < 0)
+			i += self->size;
+		if (i < 0 || i > self->size) {
+			PyErr_SetString(PyExc_IndexError,
+				"mmap index out of range");
+			return -1;
+		}
+		if (value == NULL) {
+			PyErr_SetString(PyExc_TypeError,
+				"mmap object doesn't support item deletion");
+			return -1;
+		}
+		if (!PyString_Check(value) || PyString_Size(value) != 1) {
+			PyErr_SetString(PyExc_IndexError,
+		          "mmap assignment must be single-character string");
+			return -1;
+		}
+		if (!is_writeable(self))
+			return -1;
+		buf = PyString_AsString(value);
+		self->data[i] = buf[0];
+		return 0;
+	}
+	else if (PySlice_Check(item)) {
+		Py_ssize_t start, stop, step, slicelen;
+		
+		if (PySlice_GetIndicesEx((PySliceObject *)item,
+					 self->size, &start, &stop,
+					 &step, &slicelen) < 0) {
+			return -1;
+		}
+		if (value == NULL) {
+			PyErr_SetString(PyExc_TypeError,
+				"mmap object doesn't support slice deletion");
+			return -1;
+		}
+		if (!PyString_Check(value)) {
+			PyErr_SetString(PyExc_IndexError,
+				"mmap slice assignment must be a string");
+			return -1;
+		}
+		if (PyString_Size(value) != slicelen) {
+			PyErr_SetString(PyExc_IndexError,
+				"mmap slice assignment is wrong size");
+			return -1;
+		}
+		if (!is_writeable(self))
+			return -1;
+
+		if (slicelen == 0)
+			return 0;
+		else if (step == 1) {
+			const char *buf = PyString_AsString(value);
+
+			if (buf == NULL)
+				return -1;
+			memcpy(self->data + start, buf, slicelen);
+			return 0;
+		}
+		else {
+			Py_ssize_t cur, i;
+			const char *buf = PyString_AsString(value);
+			
+			if (buf == NULL)
+				return -1;
+			for (cur = start, i = 0; i < slicelen;
+			     cur += step, i++) {
+				self->data[cur] = buf[i];
+			}
+			return 0;
+		}
+	}
+	else {
+		PyErr_SetString(PyExc_TypeError,
+				"mmap indices must be integer");
+		return -1;
+	}
+}
+
 static PySequenceMethods mmap_as_sequence = {
 	(lenfunc)mmap_length,		       /*sq_length*/
 	(binaryfunc)mmap_concat,	       /*sq_concat*/
@@ -774,6 +918,12 @@ static PySequenceMethods mmap_as_sequence = {
 	(ssizessizeobjargproc)mmap_ass_slice,      /*sq_ass_slice*/
 };
 
+static PyMappingMethods mmap_as_mapping = {
+	(lenfunc)mmap_length,
+	(binaryfunc)mmap_subscript,
+	(objobjargproc)mmap_ass_subscript,
+};
+
 static PyBufferProcs mmap_as_buffer = {
 	(readbufferproc)mmap_buffer_getreadbuf,
 	(writebufferproc)mmap_buffer_getwritebuf,
@@ -795,7 +945,7 @@ static PyTypeObject mmap_object_type = {
 	0,					/* tp_repr */
 	0,					/* tp_as_number */
 	&mmap_as_sequence,			/*tp_as_sequence*/
-	0,					/*tp_as_mapping*/
+	&mmap_as_mapping,			/*tp_as_mapping*/
 	0,					/*tp_hash*/
 	0,					/*tp_call*/
 	0,					/*tp_str*/

Objects/bufferobject.c

@@ -472,6 +472,61 @@ buffer_slice(PyBufferObject *self, Py_ssize_t left, Py_ssize_t right)
 					  right - left);
 }
 
+static PyObject *
+buffer_subscript(PyBufferObject *self, PyObject *item)
+{
+	void *p;
+	Py_ssize_t size;
+	
+	if (!get_buf(self, &p, &size, ANY_BUFFER))
+		return NULL;
+	if (PyIndex_Check(item)) {
+		Py_ssize_t i = PyNumber_AsSsize_t(item, PyExc_IndexError);
+		if (i == -1 && PyErr_Occurred())
+			return NULL;
+		if (i < 0)
+			i += size;
+		return buffer_item(self, i);
+	}
+	else if (PySlice_Check(item)) {
+		Py_ssize_t start, stop, step, slicelength, cur, i;
+
+		if (PySlice_GetIndicesEx((PySliceObject*)item, size,
+				 &start, &stop, &step, &slicelength) < 0) {
+			return NULL;
+		}
+
+		if (slicelength <= 0)
+			return PyString_FromStringAndSize("", 0);
+		else if (step == 1)
+			return PyString_FromStringAndSize((char *)p + start,
+							  stop - start);
+		else {
+			PyObject *result;
+			char *source_buf = (char *)p;
+			char *result_buf = (char *)PyMem_Malloc(slicelength);
+
+			if (result_buf == NULL)
+				return PyErr_NoMemory();
+
+			for (cur = start, i = 0; i < slicelength;
+			     cur += step, i++) {
+				result_buf[i] = source_buf[cur];
+			}
+
+			result = PyString_FromStringAndSize(result_buf,
+							    slicelength);
+			PyMem_Free(result_buf);
+			return result;
+		}
+	}
+	else {
+		PyErr_SetString(PyExc_TypeError,
+				"sequence index must be integer");
+		return NULL;
+	}
+}
+
 static int
 buffer_ass_item(PyBufferObject *self, Py_ssize_t idx, PyObject *other)
 {
@@ -581,6 +636,98 @@ buffer_ass_slice(PyBufferObject *self, Py_ssize_t left, Py_ssize_t right, PyObje
 	return 0;
 }
 
+static int
+buffer_ass_subscript(PyBufferObject *self, PyObject *item, PyObject *value)
+{
+	PyBufferProcs *pb;
+	void *ptr1, *ptr2;
+	Py_ssize_t selfsize;
+	Py_ssize_t othersize;
+
+	if ( self->b_readonly ) {
+		PyErr_SetString(PyExc_TypeError,
+				"buffer is read-only");
+		return -1;
+	}
+
+	pb = value ? value->ob_type->tp_as_buffer : NULL;
+	if ( pb == NULL ||
+	     pb->bf_getreadbuffer == NULL ||
+	     pb->bf_getsegcount == NULL )
+	{
+		PyErr_BadArgument();
+		return -1;
+	}
+	if ( (*pb->bf_getsegcount)(value, NULL) != 1 )
+	{
+		/* ### use a different exception type/message? */
+		PyErr_SetString(PyExc_TypeError,
+				"single-segment buffer object expected");
+		return -1;
+	}
+	if (!get_buf(self, &ptr1, &selfsize, ANY_BUFFER))
+		return -1;
+	if (PyIndex_Check(item)) {
+		Py_ssize_t i = PyNumber_AsSsize_t(item, PyExc_IndexError);
+		if (i == -1 && PyErr_Occurred())
+			return -1;
+		if (i < 0)
+			i += selfsize;
+		return buffer_ass_item(self, i, value);
+	}
+	else if (PySlice_Check(item)) {
+		Py_ssize_t start, stop, step, slicelength;
+		
+		if (PySlice_GetIndicesEx((PySliceObject *)item, selfsize,
+				&start, &stop, &step, &slicelength) < 0)
+			return -1;
+
+		pb = value ? value->ob_type->tp_as_buffer : NULL;
+		if (pb == NULL ||
+		    pb->bf_getreadbuffer == NULL ||
+		    pb->bf_getsegcount == NULL) {
+			PyErr_BadArgument();
+			return -1;
+		}
+		if ((*pb->bf_getsegcount)(value, NULL) != 1) {
+			/* ### use a different exception type/message? */
+			PyErr_SetString(PyExc_TypeError,
+					"single-segment buffer object expected");
+			return -1;
+		}
+		if ((othersize = (*pb->bf_getreadbuffer)(value, 0, &ptr2)) < 0)
+			return -1;
+
+		if (othersize != slicelength) {
+			PyErr_SetString(
+				PyExc_TypeError,
+				"right operand length must match slice length");
+			return -1;
+		}
+
+		if (slicelength == 0)
+			return 0;
+		else if (step == 1) {
+			memcpy((char *)ptr1 + start, ptr2, slicelength);
+			return 0;
+		}
+		else {
+			Py_ssize_t cur, i;
+			
+			for (cur = start, i = 0; i < slicelength;
+			     cur += step, i++) {
+				((char *)ptr1)[cur] = ((char *)ptr2)[i];
+			}
+
+			return 0;
+		}
+	} else {
+		PyErr_SetString(PyExc_TypeError,
+				"buffer indices must be integers");
+		return -1;
+	}
+}
+
 /* Buffer methods */
 
 static Py_ssize_t
@@ -656,6 +803,12 @@ static PySequenceMethods buffer_as_sequence = {
 	(ssizessizeobjargproc)buffer_ass_slice, /*sq_ass_slice*/
 };
 
+static PyMappingMethods buffer_as_mapping = {
+	(lenfunc)buffer_length,
+	(binaryfunc)buffer_subscript,
+	(objobjargproc)buffer_ass_subscript,
+};
+
 static PyBufferProcs buffer_as_buffer = {
 	(readbufferproc)buffer_getreadbuf,
 	(writebufferproc)buffer_getwritebuf,
@@ -676,7 +829,7 @@ PyTypeObject PyBuffer_Type = {
 	(reprfunc)buffer_repr,			/* tp_repr */
 	0,					/* tp_as_number */
 	&buffer_as_sequence,			/* tp_as_sequence */
-	0,					/* tp_as_mapping */
+	&buffer_as_mapping,			/* tp_as_mapping */
 	(hashfunc)buffer_hash,			/* tp_hash */
 	0,					/* tp_call */
 	(reprfunc)buffer_str,			/* tp_str */

Objects/listobject.c

@@ -2473,6 +2473,9 @@ list_subscript(PyListObject* self, PyObject* item)
 		if (slicelength <= 0) {
 			return PyList_New(0);
 		}
+		else if (step == 1) {
+			return list_slice(self, start, stop);
+		}
 		else {
 			result = PyList_New(slicelength);
 			if (!result) return NULL;
@@ -2516,10 +2519,15 @@ list_ass_subscript(PyListObject* self, PyObject* item, PyObject* value)
 			return -1;
 		}
 
-		/* treat L[slice(a,b)] = v _exactly_ like L[a:b] = v */
+		if (step == 1)
-		if (step == 1 && ((PySliceObject*)item)->step == Py_None)
 			return list_ass_slice(self, start, stop, value);
 
+		/* Make sure s[5:2] = [..] inserts at the right place:
+		   before 5, not before 2. */
+		if ((step < 0 && start < stop) ||
+		    (step > 0 && start > stop))
+			stop = start;
+
 		if (value == NULL) {
 			/* delete slice */
 			PyObject **garbage;
@@ -2541,12 +2549,16 @@ list_ass_subscript(PyListObject* self, PyObject* item, PyObject* value)
 				return -1;
 			}
 
-			/* drawing pictures might help
+			/* drawing pictures might help understand these for
-			   understand these for loops */
+			   loops. Basically, we memmove the parts of the
+			   list that are *not* part of the slice: step-1
+			   items for each item that is part of the slice,
+			   and then tail end of the list that was not
+			   covered by the slice */
 			for (cur = start, i = 0;
 			     cur < stop;
 			     cur += step, i++) {
-				Py_ssize_t lim = step;
+				Py_ssize_t lim = step - 1;
 
 				garbage[i] = PyList_GET_ITEM(self, cur);
 
@@ -2558,11 +2570,12 @@ list_ass_subscript(PyListObject* self, PyObject* item, PyObject* value)
 					self->ob_item + cur + 1,
 					lim * sizeof(PyObject *));
 			}
-
+			cur = start + slicelength*step;
-			for (cur = start + slicelength*step + 1;
+			if (cur < Py_Size(self)) {
-			     cur < Py_Size(self); cur++) {
+				memmove(self->ob_item + cur - slicelength,
-				PyList_SET_ITEM(self, cur - slicelength,
+					self->ob_item + cur,
-						PyList_GET_ITEM(self, cur));
+					(Py_Size(self) - cur) * 
+					 sizeof(PyObject *));
 			}
 
 			Py_Size(self) -= slicelength;
@@ -2577,7 +2590,8 @@ list_ass_subscript(PyListObject* self, PyObject* item, PyObject* value)
 		}
 		else {
 			/* assign slice */
-			PyObject **garbage, *ins, *seq, **seqitems, **selfitems;
+			PyObject *ins, *seq;
+			PyObject **garbage, **seqitems, **selfitems;
 			Py_ssize_t cur, i;
 
 			/* protect against a[::-1] = a */
@@ -2587,14 +2601,17 @@ list_ass_subscript(PyListObject* self, PyObject* item, PyObject* value)
 			}
 			else {
 				seq = PySequence_Fast(value,
-					"must assign iterable to extended slice");
+						      "must assign iterable "
+						      "to extended slice");
 			}
 			if (!seq)
 				return -1;
 
 			if (PySequence_Fast_GET_SIZE(seq) != slicelength) {
 				PyErr_Format(PyExc_ValueError,
-            "attempt to assign sequence of size %zd to extended slice of size %zd",
+					"attempt to assign sequence of "
+					"size %zd to extended slice of "
+					"size %zd",
 					     PySequence_Fast_GET_SIZE(seq),
 					     slicelength);
 				Py_DECREF(seq);

Objects/stringobject.c

@@ -1222,6 +1222,17 @@ string_subscript(PyStringObject* self, PyObject* item)
 		if (slicelength <= 0) {
 			return PyString_FromStringAndSize("", 0);
 		}
+		else if (start == 0 && step == 1 &&
+			 slicelength == PyString_GET_SIZE(self) &&
+			 PyString_CheckExact(self)) {
+			Py_INCREF(self);
+			return (PyObject *)self;
+		}
+		else if (step == 1) {
+			return PyString_FromStringAndSize(
+				PyString_AS_STRING(self) + start,
+				slicelength);
+		}
 		else {
 			source_buf = PyString_AsString((PyObject*)self);
 			result_buf = (char *)PyMem_Malloc(slicelength);

Objects/structseq.c

@@ -89,6 +89,54 @@ structseq_slice(PyStructSequence *obj, Py_ssize_t low, Py_ssize_t high)
 	return (PyObject *) np;
 }
 
+static PyObject *
+structseq_subscript(PyStructSequence *self, PyObject *item)
+{
+	if (PyIndex_Check(item)) {
+		Py_ssize_t i = PyNumber_AsSsize_t(item, PyExc_IndexError);
+		if (i == -1 && PyErr_Occurred())
+			return NULL;
+
+		if (i < 0)
+			i += VISIBLE_SIZE(self);
+
+		if (i < 0 || i >= VISIBLE_SIZE(self)) {
+			PyErr_SetString(PyExc_IndexError,
+				"tuple index out of range");
+			return NULL;
+		}
+		Py_INCREF(self->ob_item[i]);
+		return self->ob_item[i];
+	}
+	else if (PySlice_Check(item)) {
+		Py_ssize_t start, stop, step, slicelen, cur, i;
+		PyObject *result;
+		
+		if (PySlice_GetIndicesEx((PySliceObject *)item,
+					 VISIBLE_SIZE(self), &start, &stop,
+					 &step, &slicelen) < 0) {
+			return NULL;
+		}
+		if (slicelen <= 0)
+			return PyTuple_New(0);
+		result = PyTuple_New(slicelen);
+		if (result == NULL)
+			return NULL;
+		for (cur = start, i = 0; i < slicelen;
+		     cur += step, i++) {
+			PyObject *v = self->ob_item[cur];
+			Py_INCREF(v);
+			PyTuple_SET_ITEM(result, i, v);
+		}
+		return result;
+	}
+	else {
+		PyErr_SetString(PyExc_TypeError,
+				"structseq index must be integer");
+		return NULL;
+	}
+}
+
 static PyObject *
 structseq_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
 {
@@ -298,6 +346,11 @@ static PySequenceMethods structseq_as_sequence = {
 	(objobjproc)structseq_contains,	        /* sq_contains */
 };
 
+static PyMappingMethods structseq_as_mapping = {
+	(lenfunc)structseq_length,
+	(binaryfunc)structseq_subscript,
+};
+
 static PyMethodDef structseq_methods[] = {
 	{"__reduce__", (PyCFunction)structseq_reduce, 
 	 METH_NOARGS, NULL},
@@ -317,7 +370,7 @@ static PyTypeObject _struct_sequence_template = {
 	(reprfunc)structseq_repr,             	/* tp_repr */
 	0,					/* tp_as_number */
 	&structseq_as_sequence,			/* tp_as_sequence */
-	0,					/* tp_as_mapping */
+	&structseq_as_mapping,			/* tp_as_mapping */
 	structseq_hash,				/* tp_hash */
 	0,              			/* tp_call */
 	0,					/* tp_str */

Objects/tupleobject.c

@@ -603,6 +603,12 @@ tuplesubscript(PyTupleObject* self, PyObject* item)
 		if (slicelength <= 0) {
 			return PyTuple_New(0);
 		}
+		else if (start == 0 && step == 1 &&
+			 slicelength == PyTuple_GET_SIZE(self) &&
+			 PyTuple_CheckExact(self)) {
+			Py_INCREF(self);
+			return (PyObject *)self;
+		}
 		else {
 			result = PyTuple_New(slicelength);
 			if (!result) return NULL;

Objects/unicodeobject.c

@@ -7385,6 +7385,12 @@ unicode_subscript(PyUnicodeObject* self, PyObject* item)
 
         if (slicelength <= 0) {
             return PyUnicode_FromUnicode(NULL, 0);
+        } else if (start == 0 && step == 1 && slicelength == self->length &&
+                   PyUnicode_CheckExact(self)) {
+            Py_INCREF(self);
+            return (PyObject *)self;
+        } else if (step == 1) {
+            return PyUnicode_FromUnicode(self->str + start, slicelength);
         } else {
             source_buf = PyUnicode_AS_UNICODE((PyObject*)self);
             result_buf = (Py_UNICODE *)PyMem_MALLOC(slicelength*