Add `SequenceOf`/`SetOf` list-like slicing supportfix-setof-slicing

3 files changed, 44 insertions, 4 deletions

diff --git a/CHANGES.rst b/CHANGES.rst
index 26d4978..f631be5 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -1,5 +1,5 @@
 
-Revision 0.4.6, released XX-06-2019
+Revision 0.4.6, released XX-07-2019
 -----------------------------------
 
 - Added previously missing `SET OF ANY` construct encoding/decoding support.
@@ -9,6 +9,7 @@ Revision 0.4.6, released XX-06-2019
 - New elements to `SequenceOf`/`SetOf` objects can now be added at any
   position - the requirement for the new elements to reside at the end
   of the existing ones (i.e. s[len(s)] = 123) is removed.
+- List-like slicing support added to `SequenceOf`/`SetOf` objects.
 - Removed default initializer from `SequenceOf`/`SetOf` types to ensure
   consistent behaviour with the rest of ASN.1 types. Before this change,
   `SequenceOf`/`SetOf` instances immediately become value objects behaving
diff --git a/pyasn1/type/univ.py b/pyasn1/type/univ.py
index 5634f94..0ba59a7 100644
--- a/pyasn1/type/univ.py
+++ b/pyasn1/type/univ.py
@@ -1677,7 +1677,7 @@ class SequenceOfAndSetOfBase(base.AbstractConstructedAsn1Item):
                              key=key, reverse=reverse)))
 
     def __len__(self):
-        if not self._componentValues:
+        if self._componentValues is noValue or not self._componentValues:
             return 0
 
         return max(self._componentValues) + 1
@@ -1762,6 +1762,17 @@ class SequenceOfAndSetOfBase(base.AbstractConstructedAsn1Item):
             # returns noValue
             s.getComponentByPosition(0, instantiate=False)
         """
+        if isinstance(idx, slice):
+            indices = tuple(range(len(self)))
+            return [self.getComponentByPosition(subidx, default, instantiate)
+                    for subidx in indices[idx]]
+
+        if idx < 0:
+            idx = len(self) + idx
+            if idx < 0:
+                raise error.PyAsn1Error(
+                    'SequenceOf/SetOf index is out of range')
+
         try:
             componentValue = self._componentValues[idx]
 
@@ -1819,9 +1830,20 @@ class SequenceOfAndSetOfBase(base.AbstractConstructedAsn1Item):
         IndexError:
             When idx > len(self)
         """
+        if isinstance(idx, slice):
+            indices = tuple(range(len(self)))
+            startIdx = indices and indices[idx][0] or 0
+            for subIdx, subValue in enumerate(value):
+                self.setComponentByPosition(
+                    startIdx + subIdx, subValue, verifyConstraints,
+                    matchTags, matchConstraints)
+            return self
+
         if idx < 0:
-            raise error.PyAsn1Error(
-                'SequenceOf/SetOf index must not be negative')
+            idx = len(self) + idx
+            if idx < 0:
+                raise error.PyAsn1Error(
+                    'SequenceOf/SetOf index is out of range')
 
         componentType = self.componentType
 
diff --git a/tests/type/test_univ.py b/tests/type/test_univ.py
index 169b73e..de7cdee 100644
--- a/tests/type/test_univ.py
+++ b/tests/type/test_univ.py
@@ -1090,6 +1090,13 @@ class SequenceOf(BaseTestCase):
         # this is a deviation from standard sequence protocol
         assert not s[2]
 
+    def testGetItemSlice(self):
+        s = self.s1.clone()
+        s.extend(['xxx', 'yyy', 'zzz'])
+        assert s[:1] == [str2octs('xxx')]
+        assert s[-2:] == [str2octs('yyy'), str2octs('zzz')]
+        assert s[1:2] == [str2octs('yyy')]
+
     def testSetItem(self):
         s = self.s1.clone()
         s.append('xxx')
@@ -1097,6 +1104,16 @@ class SequenceOf(BaseTestCase):
         assert len(s) == 3
         assert s[1] == str2octs('')
 
+    def testSetItemSlice(self):
+        s = self.s1.clone()
+        s[:1] = ['xxx']
+        assert s == [str2octs('xxx')]
+        s[-2:] = ['yyy', 'zzz']
+        assert s == [str2octs('yyy'), str2octs('zzz')]
+        s[1:2] = ['yyy']
+        assert s == [str2octs('yyy'), str2octs('yyy')]
+        assert len(s) == 2
+
     def testAppend(self):
         self.s1.clear()
         self.s1.setComponentByPosition(0, univ.OctetString('abc'))