Add ABC ByteString which unifies bytes and bytearray (but not memoryview).

There's no ABC for "PEP 3118 style buffer API objects" because there's no
way to recognize these in Python (apart from trying to use memoryview()
on them).
Note that array.array really should be registered as a MutableSequence
but that would require importing it whenever collections is imported.

2 files changed, 26 insertions, 5 deletions

diff --git a/Lib/_abcoll.py b/Lib/_abcoll.py
index ec3e2f8..6363de9 100644
--- a/Lib/_abcoll.py
+++ b/Lib/_abcoll.py
@@ -16,6 +16,7 @@ __all__ = ["Hashable", "Iterable", "Iterator",
            "Mapping", "MutableMapping",
            "MappingView", "KeysView", "ItemsView", "ValuesView",
            "Sequence", "MutableSequence",
+           "ByteString",
            ]
 
 ### ONE-TRICK PONIES ###
@@ -489,8 +490,17 @@ class Sequence(metaclass=ABCMeta):
 
 Sequence.register(tuple)
 Sequence.register(str)
-Sequence.register(bytes)
-Sequence.register(memoryview)
+
+
+class ByteString(Sequence):
+
+    """This unifies bytes and bytearray.
+
+    XXX Should add all their methods.
+    """
+
+ByteString.register(bytes)
+ByteString.register(bytearray)
 
 
 class MutableSequence(Sequence):
@@ -531,4 +541,4 @@ class MutableSequence(Sequence):
         self.extend(values)
 
 MutableSequence.register(list)
-MutableSequence.register(bytes)
+MutableSequence.register(bytearray)  # Multiply inheriting, see ByteString
diff --git a/Lib/test/test_collections.py b/Lib/test/test_collections.py
index 3ccc06c..62da9c5 100644
--- a/Lib/test/test_collections.py
+++ b/Lib/test/test_collections.py
@@ -8,6 +8,7 @@ from collections import Sized, Container, Callable
 from collections import Set, MutableSet
 from collections import Mapping, MutableMapping
 from collections import Sequence, MutableSequence
+from collections import ByteString
 
 
 class TestNamedTuple(unittest.TestCase):
@@ -260,11 +261,21 @@ class TestCollectionABCs(unittest.TestCase):
             self.failUnless(issubclass(sample, Sequence))
         self.failUnless(issubclass(str, Sequence))
 
+    def test_ByteString(self):
+        for sample in [bytes, bytearray]:
+            self.failUnless(isinstance(sample(), ByteString))
+            self.failUnless(issubclass(sample, ByteString))
+        for sample in [str, list, tuple]:
+            self.failIf(isinstance(sample(), ByteString))
+            self.failIf(issubclass(sample, ByteString))
+        self.failIf(isinstance(memoryview(b""), ByteString))
+        self.failIf(issubclass(memoryview, ByteString))
+
     def test_MutableSequence(self):
-        for sample in [tuple, str]:
+        for sample in [tuple, str, bytes]:
             self.failIf(isinstance(sample(), MutableSequence))
             self.failIf(issubclass(sample, MutableSequence))
-        for sample in [list, bytes]:
+        for sample in [list, bytearray]:
             self.failUnless(isinstance(sample(), MutableSequence))
             self.failUnless(issubclass(sample, MutableSequence))
         self.failIf(issubclass(str, MutableSequence))