[Python] Remove Six dependency (#31264)

[Python][Remove Six] Remove Six dependency Part I

.gitignore

@@ -1,5 +1,6 @@
 # C/C++ build outputs
 .build/
+build/
 bins
 gens
 libs

src/python/grpcio/grpc/_common.py

@@ -18,7 +18,6 @@ import time
 
 import grpc
 from grpc._cython import cygrpc
-import six
 
 _LOGGER = logging.getLogger(__name__)
 
@@ -55,8 +54,8 @@ CYGRPC_STATUS_CODE_TO_STATUS_CODE = {
     cygrpc.StatusCode.data_loss: grpc.StatusCode.DATA_LOSS,
 }
 STATUS_CODE_TO_CYGRPC_STATUS_CODE = {
-    grpc_code: cygrpc_code for cygrpc_code, grpc_code in six.iteritems(
-        CYGRPC_STATUS_CODE_TO_STATUS_CODE)
+    grpc_code: cygrpc_code
+    for cygrpc_code, grpc_code in CYGRPC_STATUS_CODE_TO_STATUS_CODE.items()
 }
 
 MAXIMUM_WAIT_TIMEOUT = 0.1

src/python/grpcio/grpc/_server.py

@@ -25,7 +25,6 @@ from grpc import _common
 from grpc import _compression
 from grpc import _interceptor
 from grpc._cython import cygrpc
-import six
 
 _LOGGER = logging.getLogger(__name__)
 
@@ -276,9 +275,11 @@ class _Context(grpc.ServicerContext):
         return id_key if id_key is None else _common.decode(id_key)
 
     def auth_context(self):
+        auth_context = cygrpc.auth_context(self._rpc_event.call)
+        auth_context_dict = {} if auth_context is None else auth_context
         return {
-            _common.decode(key): value for key, value in six.iteritems(
-                cygrpc.auth_context(self._rpc_event.call))
+            _common.decode(key): value
+            for key, value in auth_context_dict.items()
         }
 
     def set_compression(self, compression):

src/python/grpcio/grpc/_utilities.py

@@ -20,7 +20,6 @@ import time
 
 import grpc
 from grpc import _common
-import six
 
 _LOGGER = logging.getLogger(__name__)
 
@@ -48,7 +47,7 @@ class DictionaryGenericHandler(grpc.ServiceRpcHandler):
         self._name = service
         self._method_handlers = {
             _common.fully_qualified_method(service, method): method_handler
-            for method, method_handler in six.iteritems(method_handlers)
+            for method, method_handler in method_handlers.items()
         }
 
     def service_name(self):

src/python/grpcio_tests/tests/unit/_api_test.py

@@ -17,7 +17,6 @@ import logging
 import unittest
 
 import grpc
-import six
 
 from tests.unit import _from_grpc_import_star
 
@@ -92,8 +91,8 @@ class AllTest(unittest.TestCase):
             'insecure_server_credentials',
         )
 
-        six.assertCountEqual(self, expected_grpc_code_elements,
-                             _from_grpc_import_star.GRPC_ELEMENTS)
+        self.assertCountEqual(expected_grpc_code_elements,
+                              _from_grpc_import_star.GRPC_ELEMENTS)
 
 
 class ChannelConnectivityTest(unittest.TestCase):

src/python/grpcio_tests/tests/unit/_auth_context_test.py

@@ -20,7 +20,6 @@ import unittest
 import grpc
 from grpc import _channel
 from grpc.experimental import session_cache
-import six
 
 from tests.unit import resources
 from tests.unit import test_common
@@ -142,7 +141,7 @@ class AuthContextTest(unittest.TestCase):
 
         auth_data = pickle.loads(response)
         auth_ctx = auth_data[_AUTH_CTX]
-        six.assertCountEqual(self, _CLIENT_IDS, auth_data[_ID])
+        self.assertCountEqual(_CLIENT_IDS, auth_data[_ID])
         self.assertEqual('x509_subject_alternative_name', auth_data[_ID_KEY])
         self.assertSequenceEqual([b'ssl'], auth_ctx['transport_security_type'])
         self.assertSequenceEqual([b'*.test.google.com'],

src/python/grpcio_tests/tests/unit/_dns_resolver_test.py

@@ -17,7 +17,6 @@ import logging
 import unittest
 
 import grpc
-import six
 
 from tests.unit import test_common
 from tests.unit.framework.common import test_constants

src/python/grpcio_tests/tests/unit/_exit_test.py

@@ -28,8 +28,6 @@ import threading
 import time
 import unittest
 
-import six
-
 from tests.unit import _exit_scenarios
 
 SCENARIO_FILE = os.path.abspath(

src/python/grpcio_tests/tests/unit/_server_wait_for_termination_test.py

@@ -21,7 +21,6 @@ import time
 import unittest
 
 import grpc
-import six
 
 from tests.unit.framework.common import test_constants
 

src/python/grpcio_tests/tests/unit/test_common.py

@@ -18,7 +18,6 @@ from concurrent import futures
 import threading
 
 import grpc
-import six
 
 INVOCATION_INITIAL_METADATA = (
     ('0', 'abc'),
@@ -64,7 +63,7 @@ def metadata_transmitted(original_metadata, transmitted_metadata):
     for key, value in transmitted_metadata:
         transmitted[key].append(value)
 
-    for key, values in six.iteritems(original):
+    for key, values in original.items():
         transmitted_values = transmitted[key]
         transmitted_iterator = iter(transmitted_values)
         try:

src/python/grpcio_tests/tests_aio/unit/auth_context_test.py

@@ -20,7 +20,6 @@ import unittest
 import grpc
 from grpc.experimental import aio
 from grpc.experimental import session_cache
-import six
 
 from tests.unit import resources
 from tests_aio.unit._test_base import AioTestBase