py3: Replace basestring with six.string_types

The builtin basestring type was removed in Python 3. Replace it with
six.string_types which works on Python 2 and Python 3.

Change-Id: Ib92a729682322cc65b41050ae169167be2899e2c

swift/common/constraints.py

@@ -133,7 +133,9 @@ def check_metadata(req, target_type):
     meta_count = 0
     meta_size = 0
     for key, value in req.headers.items():
-        if isinstance(value, basestring) and len(value) > MAX_HEADER_SIZE:
+        if (isinstance(value, six.string_types)
+           and len(value) > MAX_HEADER_SIZE):
+
             return HTTPBadRequest(body='Header value too long: %s' %
                                   key[:MAX_META_NAME_LENGTH],
                                   request=req, content_type='text/plain')

swift/common/direct_client.py

@@ -23,6 +23,7 @@ import socket
 from time import time
 
 from eventlet import sleep, Timeout
+import six
 from six.moves.http_client import HTTPException
 
 from swift.common.bufferedhttp import http_connect
@@ -399,7 +400,7 @@ def direct_put_object(node, part, account, container, name, contents,
         headers['Content-Type'] = 'application/octet-stream'
     if not contents:
         headers['Content-Length'] = '0'
-    if isinstance(contents, basestring):
+    if isinstance(contents, six.string_types):
         contents = [contents]
     # Incase the caller want to insert an object with specific age
     add_ts = 'X-Timestamp' not in headers

swift/common/middleware/tempauth.py

@@ -23,6 +23,7 @@ import hmac
 import base64
 
 from eventlet import Timeout
+import six
 from six.moves.urllib.parse import unquote
 from swift.common.swob import Response, Request
 from swift.common.swob import HTTPBadRequest, HTTPForbidden, HTTPNotFound, \
@@ -460,7 +461,7 @@ class TempAuth(object):
             if not isinstance(result[key], list):
                 return "Value for key '%s' must be a list" % key
             for grantee in result[key]:
-                if not isinstance(grantee, basestring):
+                if not isinstance(grantee, six.string_types):
                     return "Elements of '%s' list must be strings" % key
 
         # Everything looks fine, no errors found

test/unit/cli/test_ringbuilder.py

@@ -30,7 +30,7 @@ from swift.common.ring import RingBuilder
 class RunSwiftRingBuilderMixin(object):
 
     def run_srb(self, *argv):
-        if len(argv) == 1 and isinstance(argv[0], basestring):
+        if len(argv) == 1 and isinstance(argv[0], six.string_types):
             # convert a single string to a list
             argv = shlex.split(argv[0])
         mock_stdout = six.StringIO()