[python3] string class comparison using six

setup.py

@@ -24,6 +24,7 @@ setup(
 
     install_requires=[
       'setuptools',
+      'six',  # py2/3 compatibility library
       'bob',  # base signal proc./machine learning library
       'xbob.db.verification.utils>=0.1.4' # defines a set of utilities for face verification databases like this one.
     ],

xbob/db/banca/query.py

@@ -7,6 +7,7 @@ BANCA database in the most obvious ways.
 """
 
 import os
+import six
 from bob.db import utils
 from .models import *
 from .driver import Interface
@@ -31,7 +32,7 @@ class Database(xbob.db.verification.utils.SQLiteDatabase, xbob.db.verification.u
     """Replace 'dev' by 'g1' and 'eval' by 'g2' in a list of groups, and
        returns the new list"""
     if not l: return l
-    elif isinstance(l, str): return self.__group_replace_alias__((l,))
+    elif isinstance(l, six.string_types): return self.__group_replace_alias__((l,))
     l2 = []
     for val in l:
       if(val == 'dev'): l2.append('g1')