Added documentation for BYTES caster

NEWS

@@ -9,6 +9,8 @@ New features:
 - Added `~psycopg2.errors` module. Every PostgreSQL error is converted into
   a specific exception class (:ticket:`#682`).
 - Added `~psycopg2.extensions.encrypt_password()` function (:ticket:`#576`).
+- Added `~psycopg2.extensions.BYTES` adapter to manage databases with mixed
+  encodings on Python 3 (:ticket:`#835`).
 - Added `~psycopg2.extensions.Column.table_oid` and
   `~psycopg2.extensions.Column.table_column` attributes on `cursor.description`
   items (:ticket:`#661`).

doc/src/extensions.rst

@@ -947,6 +947,7 @@ Python objects.  All the typecasters are automatically registered, except
 from the database.  See :ref:`unicode-handling` for details.
 
 .. data:: BOOLEAN
+          BYTES
           DATE
           DECIMAL
           FLOAT
@@ -963,6 +964,7 @@ from the database.  See :ref:`unicode-handling` for details.
 
 .. data:: BINARYARRAY
           BOOLEANARRAY
+          BYTESARRAY
           DATEARRAY
           DATETIMEARRAY
           DECIMALARRAY
@@ -1011,5 +1013,8 @@ from the database.  See :ref:`unicode-handling` for details.
         module. In older versions they can be imported from the implementation
         module `!psycopg2._psycopg`.
 
-.. versionchanged:: 2.7.2
-        added `!*DATETIMETZ*` objects.
+.. versionadded:: 2.7.2
+    the `!*DATETIMETZ*` objects.
+
+.. versionadded:: 2.8
+    the `!BYTES` and `BYTESARRAY` objects.

doc/src/faq.rst

@@ -108,6 +108,19 @@ My database is Unicode, but I receive all the strings as UTF-8 `!str`. Can I rec
     See :ref:`unicode-handling` for the gory details.
 
 
+.. _faq-bytes:
+.. cssclass:: faq
+
+My database is in mixed encoding. My program was working on Python 2 but Python 3 fails decoding the strings. How do I avoid decoding?
+    From psycopg 2.8 you can use the following adapters to always return bytes
+    from strings::
+
+        psycopg2.extensions.register_type(psycopg2.extensions.BYTES)
+        psycopg2.extensions.register_type(psycopg2.extensions.BYTESARRAY)
+
+    See :ref:`unicode-handling` for an example.
+
+
 .. _faq-float:
 .. cssclass:: faq
 

doc/src/usage.rst

@@ -457,13 +457,29 @@ the connection or globally: see the function
     Unicode, you can register the related typecasters globally as soon as
     Psycopg is imported::
 
-        import psycopg2
         import psycopg2.extensions
         psycopg2.extensions.register_type(psycopg2.extensions.UNICODE)
         psycopg2.extensions.register_type(psycopg2.extensions.UNICODEARRAY)
 
     and forget about this story.
 
+.. note::
+
+    In some cases, on Python 3, you may want to receive `!bytes` instead of
+    `!str`, without undergoing to any decoding. This is especially the case if
+    the data in the database is in mixed encoding. The
+    `~psycopg2.extensions.BYTES` caster is what you neeed::
+
+        import psycopg2.extensions
+        psycopg2.extensions.register_type(psycopg2.extensions.BYTES, conn)
+        psycopg2.extensions.register_type(psycopg2.extensions.BYTESARRAY, conn)
+        cur = conn.cursor()
+        cur.execute("select %s::text", (u"€",))
+        cur.fetchone()[0]
+        b'\xe2\x82\xac'
+
+    .. versionadded: 2.8
+
 
 .. index::
     single: Buffer; Adaptation