use buffer on py2, memoryview on py3

This wouldn't be necessary if the sqlite module accepted memoryview
instances on py2, but it doesn't.

beets/dbcore/query.py

@@ -25,6 +25,9 @@ import unicodedata
 from functools import reduce
 import six
 
+if not six.PY2:
+    buffer = memoryview  # sqlite won't accept memoryview in python 2
+
 
 class ParsingError(ValueError):
     """Abstract class for any unparseable user-requested album/query
@@ -244,7 +247,7 @@ class BytesQuery(MatchQuery):
     def __init__(self, field, pattern):
         super(BytesQuery, self).__init__(field, pattern)
 
-        # Use a buffer representation of the pattern for SQLite
+        # Use a buffer/memoryview representation of the pattern for SQLite
         # matching. This instructs SQLite to treat the blob as binary
         # rather than encoded Unicode.
         if isinstance(self.pattern, (six.text_type, bytes)):

beets/dbcore/types.py

@@ -21,6 +21,9 @@ from . import query
 from beets.util import str2bool
 import six
 
+if not six.PY2:
+    buffer = memoryview  # sqlite won't accept memoryview in python 2
+
 
 # Abstract base.
 
@@ -98,8 +101,8 @@ class Type(object):
         https://docs.python.org/2/library/sqlite3.html#sqlite-and-python-types
 
         Flexible fields have the type affinity `TEXT`. This means the
-        `sql_value` is either a `buffer` or a `unicode` object` and the
-        method must handle these in addition.
+        `sql_value` is either a `buffer`/`memoryview` or a `unicode` object`
+        and the method must handle these in addition.
         """
         if isinstance(sql_value, buffer):
             sql_value = bytes(sql_value).decode('utf8', 'ignore')

beets/library.py

@@ -35,6 +35,8 @@ from beets import dbcore
 from beets.dbcore import types
 import beets
 
+if not six.PY2:
+    buffer = memoryview  # sqlite won't accept memoryview in python 2
 
 log = logging.getLogger('beets')
 
@@ -159,8 +161,8 @@ class PathType(types.Type):
             return bytestring_path(value)
 
         elif isinstance(value, buffer):
-            # SQLite must store bytestings as buffers to avoid decoding.
-            # We unwrap buffers to bytes.
+            # SQLite must store bytestings as buffers/memoryview
+            # to avoid decoding. We unwrap buffers to bytes.
             return bytes(value)
 
         else:

beets/util/__init__.py

@@ -633,9 +633,13 @@ def as_string(value):
     """Convert a value to a Unicode object for matching with a query.
     None becomes the empty string. Bytestrings are silently decoded.
     """
+    buffer_types = memoryview
+    if six.PY2:
+        buffer_types = (buffer, memoryview)
+
     if value is None:
         return u''
-    elif isinstance(value, buffer):
+    elif isinstance(value, buffer_types):
         return bytes(value).decode('utf8', 'ignore')
     elif isinstance(value, bytes):
         return value.decode('utf8', 'ignore')