Initial Python3 support

Notable Changes:
  -Convert all str types to byte types at cython layer (ascii encoding)
  -Use six for packages that have different names in Python2/Python3
  -By default, unit tests are compiled/run in Python2.7 and Python3.4
  -Ensure MACOSX_BUILD_TARGET is at least 10.7

27 files changed, 194 insertions, 222 deletions

diff --git a/src/python/grpcio/commands.py b/src/python/grpcio/commands.py
index 295dab2d27..3e974eba0a 100644
--- a/src/python/grpcio/commands.py
+++ b/src/python/grpcio/commands.py
@@ -191,7 +191,7 @@ class BuildProtoModules(setuptools.Command):
       except subprocess.CalledProcessError as e:
         sys.stderr.write(
             'warning: Command:\n{}\nMessage:\n{}\nOutput:\n{}'.format(
-                command, e.message, e.output))
+                command, str(e), e.output))
 
     # Generated proto directories dont include __init__.py, but
     # these are needed for python package resolution
diff --git a/src/python/grpcio/grpc/_channel.py b/src/python/grpcio/grpc/_channel.py
index d9eb5a4b77..555a92a363 100644
--- a/src/python/grpcio/grpc/_channel.py
+++ b/src/python/grpcio/grpc/_channel.py
@@ -85,7 +85,7 @@ def _deadline(timeout):
 
 
 def _unknown_code_details(unknown_cygrpc_code, details):
-  return b'Server sent unknown code {} and details "{}"'.format(
+  return 'Server sent unknown code {} and details "{}"'.format(
       unknown_cygrpc_code, details)
 
 
@@ -142,7 +142,7 @@ def _handle_event(event, state, response_deserializer):
         response = _common.deserialize(
             serialized_response, response_deserializer)
         if response is None:
-          details = b'Exception deserializing response!'
+          details = 'Exception deserializing response!'
           _abort(state, grpc.StatusCode.INTERNAL, details)
         else:
           state.response = response
@@ -186,7 +186,7 @@ def _consume_request_iterator(
         if state.code is None and not state.cancelled:
           if serialized_request is None:
             call.cancel()
-            details = b'Exception serializing request!'
+            details = 'Exception serializing request!'
             _abort(state, grpc.StatusCode.INTERNAL, details)
             return
           else:
@@ -230,7 +230,7 @@ class _Rendezvous(grpc.RpcError, grpc.Future, grpc.Call):
       if self._state.code is None:
         self._call.cancel()
         self._state.cancelled = True
-        _abort(self._state, grpc.StatusCode.CANCELLED, b'Cancelled!')
+        _abort(self._state, grpc.StatusCode.CANCELLED, 'Cancelled!')
         self._state.condition.notify_all()
       return False
 
@@ -402,7 +402,7 @@ def _start_unary_request(request, timeout, request_serializer):
   if serialized_request is None:
     state = _RPCState(
         (), _EMPTY_METADATA, _EMPTY_METADATA, grpc.StatusCode.INTERNAL,
-        b'Exception serializing request!')
+        'Exception serializing request!')
     rendezvous = _Rendezvous(state, None, None, deadline)
     return deadline, deadline_timespec, None, rendezvous
   else:
diff --git a/src/python/grpcio/grpc/_common.py b/src/python/grpcio/grpc/_common.py
index a3fb66cd07..b8688a0149 100644
--- a/src/python/grpcio/grpc/_common.py
+++ b/src/python/grpcio/grpc/_common.py
@@ -97,3 +97,16 @@ def serialize(message, serializer):
 def deserialize(serialized_message, deserializer):
   return _transform(serialized_message, deserializer,
                     'Exception deserializing message!')
+
+
+def _encode(s):
+  if isinstance(s, bytes):
+    return s
+  else:
+    return s.encode('ascii')
+
+
+def fully_qualified_method(group, method):
+  group = _encode(group)
+  method = _encode(method)
+  return b'/' + group + b'/' + method
diff --git a/src/python/grpcio/grpc/_cython/_cygrpc/call.pyx.pxi b/src/python/grpcio/grpc/_cython/_cygrpc/call.pyx.pxi
index 1bfe6344e0..a09bbc75fe 100644
--- a/src/python/grpcio/grpc/_cython/_cygrpc/call.pyx.pxi
+++ b/src/python/grpcio/grpc/_cython/_cygrpc/call.pyx.pxi
@@ -55,6 +55,7 @@ cdef class Call:
   def cancel(
       self, grpc_status_code error_code=GRPC_STATUS__DO_NOT_USE,
       details=None):
+    details = str_to_bytes(details)
     if not self.is_valid:
       raise ValueError("invalid call object cannot be used from Python")
     if (details is None) != (error_code == GRPC_STATUS__DO_NOT_USE):
@@ -63,12 +64,6 @@ cdef class Call:
     cdef grpc_call_error result
     cdef char *c_details = NULL
     if error_code != GRPC_STATUS__DO_NOT_USE:
-      if isinstance(details, bytes):
-        pass
-      elif isinstance(details, basestring):
-        details = details.encode()
-      else:
-        raise TypeError("expected details to be str or bytes")
       self.references.append(details)
       c_details = details
       with nogil:
diff --git a/src/python/grpcio/grpc/_cython/_cygrpc/channel.pyx.pxi b/src/python/grpcio/grpc/_cython/_cygrpc/channel.pyx.pxi
index c26bc083cf..866cff0d01 100644
--- a/src/python/grpcio/grpc/_cython/_cygrpc/channel.pyx.pxi
+++ b/src/python/grpcio/grpc/_cython/_cygrpc/channel.pyx.pxi
@@ -34,18 +34,13 @@ cdef class Channel:
 
   def __cinit__(self, target, ChannelArgs arguments=None,
                 ChannelCredentials channel_credentials=None):
+    target = str_to_bytes(target)
     cdef grpc_channel_args *c_arguments = NULL
     cdef char *c_target = NULL
     self.c_channel = NULL
     self.references = []
     if arguments is not None:
       c_arguments = &arguments.c_args
-    if isinstance(target, bytes):
-      pass
-    elif isinstance(target, basestring):
-      target = target.encode()
-    else:
-      raise TypeError("expected target to be str or bytes")
     c_target = target
     if channel_credentials is None:
       with nogil:
@@ -62,25 +57,14 @@ cdef class Channel:
   def create_call(self, Call parent, int flags,
                   CompletionQueue queue not None,
                   method, host, Timespec deadline not None):
+    method = str_to_bytes(method)
+    host = str_to_bytes(host)
     if queue.is_shutting_down:
       raise ValueError("queue must not be shutting down or shutdown")
-    if isinstance(method, bytes):
-      pass
-    elif isinstance(method, basestring):
-      method = method.encode()
-    else:
-      raise TypeError("expected method to be str or bytes")
     cdef char *method_c_string = method
     cdef char *host_c_string = NULL
-    if host is None:
-      pass
-    elif isinstance(host, bytes):
+    if host is not None:
       host_c_string = host
-    elif isinstance(host, basestring):
-      host = host.encode()
-      host_c_string = host
-    else:
-      raise TypeError("expected host to be str, bytes, or None")
     cdef Call operation_call = Call()
     operation_call.references = [self, method, host, queue]
     cdef grpc_call *parent_call = NULL
diff --git a/src/python/grpcio/grpc/_cython/_cygrpc/credentials.pxd.pxi b/src/python/grpcio/grpc/_cython/_cygrpc/credentials.pxd.pxi
index 19a59e08f3..d377a67520 100644
--- a/src/python/grpcio/grpc/_cython/_cygrpc/credentials.pxd.pxi
+++ b/src/python/grpcio/grpc/_cython/_cygrpc/credentials.pxd.pxi
@@ -54,7 +54,7 @@ cdef class ServerCredentials:
 cdef class CredentialsMetadataPlugin:
 
   cdef object plugin_callback
-  cdef str plugin_name
+  cdef bytes plugin_name
 
   cdef grpc_metadata_credentials_plugin make_c_plugin(self)
 
diff --git a/src/python/grpcio/grpc/_cython/_cygrpc/credentials.pyx.pxi b/src/python/grpcio/grpc/_cython/_cygrpc/credentials.pyx.pxi
index 1ba86457af..470382d609 100644
--- a/src/python/grpcio/grpc/_cython/_cygrpc/credentials.pyx.pxi
+++ b/src/python/grpcio/grpc/_cython/_cygrpc/credentials.pyx.pxi
@@ -82,7 +82,7 @@ cdef class ServerCredentials:
 
 cdef class CredentialsMetadataPlugin:
 
-  def __cinit__(self, object plugin_callback, str name):
+  def __cinit__(self, object plugin_callback, name):
     """
     Args:
       plugin_callback (callable): Callback accepting a service URL (str/bytes)
@@ -93,6 +93,7 @@ cdef class CredentialsMetadataPlugin:
         successful).
       name (str): Plugin name.
     """
+    name = str_to_bytes(name)
     if not callable(plugin_callback):
       raise ValueError('expected callable plugin_callback')
     self.plugin_callback = plugin_callback
@@ -129,7 +130,8 @@ cdef void plugin_get_metadata(
     grpc_credentials_plugin_metadata_cb cb, void *user_data) with gil:
   def python_callback(
       Metadata metadata, grpc_status_code status,
-      const char *error_details):
+      error_details):
+    error_details = str_to_bytes(error_details)
     cb(user_data, metadata.c_metadata_array.metadata,
        metadata.c_metadata_array.count, status, error_details)
   cdef CredentialsMetadataPlugin self = <CredentialsMetadataPlugin>state
@@ -148,14 +150,7 @@ def channel_credentials_google_default():
 
 def channel_credentials_ssl(pem_root_certificates,
                             SslPemKeyCertPair ssl_pem_key_cert_pair):
-  if pem_root_certificates is None:
-    pass
-  elif isinstance(pem_root_certificates, bytes):
-    pass
-  elif isinstance(pem_root_certificates, basestring):
-    pem_root_certificates = pem_root_certificates.encode()
-  else:
-    raise TypeError("expected str or bytes for pem_root_certificates")
+  pem_root_certificates = str_to_bytes(pem_root_certificates)
   cdef ChannelCredentials credentials = ChannelCredentials()
   cdef const char *c_pem_root_certificates = NULL
   if pem_root_certificates is not None:
@@ -207,12 +202,7 @@ def call_credentials_google_compute_engine():
 
 def call_credentials_service_account_jwt_access(
     json_key, Timespec token_lifetime not None):
-  if isinstance(json_key, bytes):
-    pass
-  elif isinstance(json_key, basestring):
-    json_key = json_key.encode()
-  else:
-    raise TypeError("expected json_key to be str or bytes")
+  json_key = str_to_bytes(json_key)
   cdef CallCredentials credentials = CallCredentials()
   cdef char *json_key_c_string = json_key
   with nogil:
@@ -223,12 +213,7 @@ def call_credentials_service_account_jwt_access(
   return credentials
 
 def call_credentials_google_refresh_token(json_refresh_token):
-  if isinstance(json_refresh_token, bytes):
-    pass
-  elif isinstance(json_refresh_token, basestring):
-    json_refresh_token = json_refresh_token.encode()
-  else:
-    raise TypeError("expected json_refresh_token to be str or bytes")
+  json_refresh_token = str_to_bytes(json_refresh_token)
   cdef CallCredentials credentials = CallCredentials()
   cdef char *json_refresh_token_c_string = json_refresh_token
   with nogil:
@@ -238,18 +223,8 @@ def call_credentials_google_refresh_token(json_refresh_token):
   return credentials
 
 def call_credentials_google_iam(authorization_token, authority_selector):
-  if isinstance(authorization_token, bytes):
-    pass
-  elif isinstance(authorization_token, basestring):
-    authorization_token = authorization_token.encode()
-  else:
-    raise TypeError("expected authorization_token to be str or bytes")
-  if isinstance(authority_selector, bytes):
-    pass
-  elif isinstance(authority_selector, basestring):
-    authority_selector = authority_selector.encode()
-  else:
-    raise TypeError("expected authority_selector to be str or bytes")
+  authorization_token = str_to_bytes(authorization_token)
+  authority_selector = str_to_bytes(authority_selector)
   cdef CallCredentials credentials = CallCredentials()
   cdef char *authorization_token_c_string = authorization_token
   cdef char *authority_selector_c_string = authority_selector
@@ -272,16 +247,10 @@ def call_credentials_metadata_plugin(CredentialsMetadataPlugin plugin):
 
 def server_credentials_ssl(pem_root_certs, pem_key_cert_pairs,
                            bint force_client_auth):
+  pem_root_certs = str_to_bytes(pem_root_certs)
   cdef char *c_pem_root_certs = NULL
-  if pem_root_certs is None:
-    pass
-  elif isinstance(pem_root_certs, bytes):
-    c_pem_root_certs = pem_root_certs
-  elif isinstance(pem_root_certs, basestring):
-    pem_root_certs = pem_root_certs.encode()
+  if pem_root_certs is not None: 
     c_pem_root_certs = pem_root_certs
-  else:
-    raise TypeError("expected pem_root_certs to be str or bytes")
   pem_key_cert_pairs = list(pem_key_cert_pairs)
   for pair in pem_key_cert_pairs:
     if not isinstance(pair, SslPemKeyCertPair):
diff --git a/src/python/grpcio/grpc/_cython/_cygrpc/grpc_string.pyx.pxi b/src/python/grpcio/grpc/_cython/_cygrpc/grpc_string.pyx.pxi
new file mode 100644
index 0000000000..274f038e0a
--- /dev/null
+++ b/src/python/grpcio/grpc/_cython/_cygrpc/grpc_string.pyx.pxi
@@ -0,0 +1,39 @@
+# Copyright 2016, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+
+# This function will ascii encode unicode string inputs if neccesary.
+# In Python3, unicode strings are the default str type.
+cdef bytes str_to_bytes(object s):
+  if s is None or isinstance(s, bytes):
+    return s
+  elif isinstance(s, unicode):
+    return s.encode('ascii')
+  else:
+    raise TypeError('Expected bytes, str, or unicode, not {}'.format(type(s)))
diff --git a/src/python/grpcio/grpc/_cython/_cygrpc/records.pyx.pxi b/src/python/grpcio/grpc/_cython/_cygrpc/records.pyx.pxi
index e0219b0086..2e52953c0a 100644
--- a/src/python/grpcio/grpc/_cython/_cygrpc/records.pyx.pxi
+++ b/src/python/grpcio/grpc/_cython/_cygrpc/records.pyx.pxi
@@ -235,18 +235,13 @@ cdef class ByteBuffer:
     if data is None:
       self.c_byte_buffer = NULL
       return
-    if isinstance(data, bytes):
-      pass
-    elif isinstance(data, basestring):
-      data = data.encode()
-    elif isinstance(data, ByteBuffer):
+    if isinstance(data, ByteBuffer):
       data = (<ByteBuffer>data).bytes()
       if data is None:
         self.c_byte_buffer = NULL
         return
     else:
-      raise TypeError("expected value to be of type str, bytes, or "
-                      "ByteBuffer, not {}".format(type(data)))
+      data = str_to_bytes(data)
 
     cdef char *c_data = data
     cdef gpr_slice data_slice
@@ -302,19 +297,8 @@ cdef class ByteBuffer:
 cdef class SslPemKeyCertPair:
 
   def __cinit__(self, private_key, certificate_chain):
-    if isinstance(private_key, bytes):
-      self.private_key = private_key
-    elif isinstance(private_key, basestring):
-      self.private_key = private_key.encode()
-    else:
-      raise TypeError("expected private_key to be of type str or bytes")
-    if isinstance(certificate_chain, bytes):
-      self.certificate_chain = certificate_chain
-    elif isinstance(certificate_chain, basestring):
-      self.certificate_chain = certificate_chain.encode()
-    else:
-      raise TypeError("expected certificate_chain to be of type str or bytes "
-                      "or int")
+    self.private_key = str_to_bytes(private_key)
+    self.certificate_chain = str_to_bytes(certificate_chain)
     self.c_pair.private_key = self.private_key
     self.c_pair.certificate_chain = self.certificate_chain
 
@@ -322,27 +306,16 @@ cdef class SslPemKeyCertPair:
 cdef class ChannelArg:
 
   def __cinit__(self, key, value):
-    if isinstance(key, bytes):
-      self.key = key
-    elif isinstance(key, basestring):
-      self.key = key.encode()
-    else:
-      raise TypeError("expected key to be of type str or bytes")
-    if isinstance(value, bytes):
-      self.value = value
-      self.c_arg.type = GRPC_ARG_STRING
-      self.c_arg.value.string = self.value
-    elif isinstance(value, basestring):
-      self.value = value.encode()
-      self.c_arg.type = GRPC_ARG_STRING
-      self.c_arg.value.string = self.value
-    elif isinstance(value, int):
+    self.key = str_to_bytes(key)
+    self.c_arg.key = self.key
+    if isinstance(value, int):
       self.value = int(value)
       self.c_arg.type = GRPC_ARG_INTEGER
       self.c_arg.value.integer = self.value
     else:
-      raise TypeError("expected value to be of type str or bytes or int")
-    self.c_arg.key = self.key
+      self.value = str_to_bytes(value)
+      self.c_arg.type = GRPC_ARG_STRING
+      self.c_arg.value.string = self.value
 
 
 cdef class ChannelArgs:
@@ -375,18 +348,8 @@ cdef class ChannelArgs:
 cdef class Metadatum:
 
   def __cinit__(self, key, value):
-    if isinstance(key, bytes):
-      self._key = key
-    elif isinstance(key, basestring):
-      self._key = key.encode()
-    else:
-      raise TypeError("expected key to be of type str or bytes")
-    if isinstance(value, bytes):
-      self._value = value
-    elif isinstance(value, basestring):
-      self._value = value.encode()
-    else:
-      raise TypeError("expected value to be of type str or bytes")
+    self._key = str_to_bytes(key)
+    self._value = str_to_bytes(value)
     self.c_metadata.key = self._key
     self.c_metadata.value = self._value
     self.c_metadata.value_length = len(self._value)
@@ -601,12 +564,7 @@ def operation_send_close_from_client(int flags):
 
 def operation_send_status_from_server(
     Metadata metadata, grpc_status_code code, details, int flags):
-  if isinstance(details, bytes):
-    pass
-  elif isinstance(details, basestring):
-    details = details.encode()
-  else:
-    raise TypeError("expected a str or bytes object for details")
+  details = str_to_bytes(details)
   cdef Operation op = Operation()
   op.c_op.type = GRPC_OP_SEND_STATUS_FROM_SERVER
   op.c_op.flags = flags
diff --git a/src/python/grpcio/grpc/_cython/_cygrpc/server.pyx.pxi b/src/python/grpcio/grpc/_cython/_cygrpc/server.pyx.pxi
index 55948755b2..c8a73e65d6 100644
--- a/src/python/grpcio/grpc/_cython/_cygrpc/server.pyx.pxi
+++ b/src/python/grpcio/grpc/_cython/_cygrpc/server.pyx.pxi
@@ -103,12 +103,7 @@ cdef class Server:
 
   def add_http2_port(self, address,
                      ServerCredentials server_credentials=None):
-    if isinstance(address, bytes):
-      pass
-    elif isinstance(address, basestring):
-      address = address.encode()
-    else:
-      raise TypeError("expected address to be a str or bytes")
+    address = str_to_bytes(address)
     self.references.append(address)
     cdef int result
     cdef char *address_c_string = address
diff --git a/src/python/grpcio/grpc/_cython/cygrpc.pyx b/src/python/grpcio/grpc/_cython/cygrpc.pyx
index 8823ea5ef5..cf146f5a04 100644
--- a/src/python/grpcio/grpc/_cython/cygrpc.pyx
+++ b/src/python/grpcio/grpc/_cython/cygrpc.pyx
@@ -35,6 +35,7 @@ import sys
 
 # TODO(atash): figure out why the coverage tool gets confused about the Cython
 # coverage plugin when the following files don't have a '.pxi' suffix.
+include "grpc/_cython/_cygrpc/grpc_string.pyx.pxi"
 include "grpc/_cython/_cygrpc/call.pyx.pxi"
 include "grpc/_cython/_cygrpc/channel.pyx.pxi"
 include "grpc/_cython/_cygrpc/credentials.pyx.pxi"
diff --git a/src/python/grpcio/grpc/_links/service.py b/src/python/grpcio/grpc/_links/service.py
index 11310e2240..5fc4994ca0 100644
--- a/src/python/grpcio/grpc/_links/service.py
+++ b/src/python/grpcio/grpc/_links/service.py
@@ -33,6 +33,7 @@ import abc
 import enum
 import logging
 import threading
+import six
 import time
 
 from grpc._adapter import _intermediary_low
@@ -177,7 +178,10 @@ class _Kernel(object):
     call = service_acceptance.call
     call.accept(self._completion_queue, call)
     try:
-      group, method = service_acceptance.method.split(b'/')[1:3]
+      service_method = service_acceptance.method
+      if six.PY3:
+          service_method = service_method.decode('latin1')
+      group, method = service_method.split('/')[1:3]
     except ValueError:
       logging.info('Illegal path "%s"!', service_acceptance.method)
       return
diff --git a/src/python/grpcio/grpc/_server.py b/src/python/grpcio/grpc/_server.py
index aae9f48ae6..f4f6720497 100644
--- a/src/python/grpcio/grpc/_server.py
+++ b/src/python/grpcio/grpc/_server.py
@@ -85,7 +85,7 @@ def _abortion_code(state, code):
 
 
 def _details(state):
-  return b'' if state.details is None else state.details
+  return '' if state.details is None else state.details
 
 
 class _HandlerCallDetails(
@@ -189,7 +189,7 @@ def _receive_message(state, call, request_deserializer):
         if request is None:
           _abort(
               state, call, cygrpc.StatusCode.internal,
-              b'Exception deserializing request!')
+              'Exception deserializing request!')
         else:
           state.request = request
         state.condition.notify_all()
@@ -340,7 +340,7 @@ def _unary_request(rpc_event, state, request_deserializer):
           state.condition.wait()
           if state.request is None:
             if state.client is _CLOSED:
-              details = b'"{}" requires exactly one request message.'.format(
+              details = '"{}" requires exactly one request message.'.format(
                   rpc_event.request_call_details.method)
               # TODO(5992#issuecomment-220761992): really, what status code?
               _abort(
@@ -363,7 +363,7 @@ def _call_behavior(rpc_event, state, behavior, argument, request_deserializer):
   except Exception as e:  # pylint: disable=broad-except
     with state.condition:
       if e not in state.rpc_errors:
-        details = b'Exception calling application: {}'.format(e)
+        details = 'Exception calling application: {}'.format(e)
         logging.exception(details)
         _abort(
             state, rpc_event.operation_call, cygrpc.StatusCode.unknown, details)
@@ -378,7 +378,7 @@ def _take_response_from_response_iterator(rpc_event, state, response_iterator):
   except Exception as e:  # pylint: disable=broad-except
     with state.condition:
       if e not in state.rpc_errors:
-        details = b'Exception iterating responses: {}'.format(e)
+        details = 'Exception iterating responses: {}'.format(e)
         logging.exception(details)
         _abort(
             state, rpc_event.operation_call, cygrpc.StatusCode.unknown, details)
@@ -391,7 +391,7 @@ def _serialize_response(rpc_event, state, response, response_serializer):
     with state.condition:
       _abort(
           state, rpc_event.operation_call, cygrpc.StatusCode.internal,
-          b'Failed to serialize response!')
+          'Failed to serialize response!')
     return None
   else:
     return serialized_response
@@ -544,7 +544,7 @@ def _handle_unrecognized_method(rpc_event):
       cygrpc.operation_receive_close_on_server(_EMPTY_FLAGS),
       cygrpc.operation_send_status_from_server(
           _EMPTY_METADATA, cygrpc.StatusCode.unimplemented,
-          b'Method not found!', _EMPTY_FLAGS),
+          'Method not found!', _EMPTY_FLAGS),
   )
   rpc_state = _RPCState()
   rpc_event.operation_call.start_batch(
diff --git a/src/python/grpcio/grpc/beta/_client_adaptations.py b/src/python/grpcio/grpc/beta/_client_adaptations.py
index 621fcf2174..024808c540 100644
--- a/src/python/grpcio/grpc/beta/_client_adaptations.py
+++ b/src/python/grpcio/grpc/beta/_client_adaptations.py
@@ -30,6 +30,7 @@
 """Translates gRPC's client-side API into gRPC's client-side Beta API."""
 
 import grpc
+from grpc import _common
 from grpc._cython import cygrpc
 from grpc.beta import interfaces
 from grpc.framework.common import cardinality
@@ -48,10 +49,6 @@ _STATUS_CODE_TO_ABORTION_KIND_AND_ABORTION_ERROR_CLASS = {
 }
 
 
-def _fully_qualified_method(group, method):
-  return b'/{}/{}'.format(group, method)
-
-
 def _effective_metadata(metadata, metadata_transformer):
   non_none_metadata = () if metadata is None else metadata
   if metadata_transformer is None:
@@ -184,7 +181,7 @@ def _blocking_unary_unary(
     metadata_transformer, request, request_serializer, response_deserializer):
   try:
     multi_callable = channel.unary_unary(
-        _fully_qualified_method(group, method),
+        _common.fully_qualified_method(group, method),
         request_serializer=request_serializer,
         response_deserializer=response_deserializer)
     effective_metadata = _effective_metadata(metadata, metadata_transformer)
@@ -205,7 +202,7 @@ def _future_unary_unary(
     channel, group, method, timeout, protocol_options, metadata,
     metadata_transformer, request, request_serializer, response_deserializer):
   multi_callable = channel.unary_unary(
-      _fully_qualified_method(group, method),
+      _common.fully_qualified_method(group, method),
       request_serializer=request_serializer,
       response_deserializer=response_deserializer)
   effective_metadata = _effective_metadata(metadata, metadata_transformer)
@@ -219,7 +216,7 @@ def _unary_stream(
     channel, group, method, timeout, protocol_options, metadata,
     metadata_transformer, request, request_serializer, response_deserializer):
   multi_callable = channel.unary_stream(
-      _fully_qualified_method(group, method),
+      _common.fully_qualified_method(group, method),
       request_serializer=request_serializer,
       response_deserializer=response_deserializer)
   effective_metadata = _effective_metadata(metadata, metadata_transformer)
@@ -235,7 +232,7 @@ def _blocking_stream_unary(
     response_deserializer):
   try:
     multi_callable = channel.stream_unary(
-        _fully_qualified_method(group, method),
+        _common.fully_qualified_method(group, method),
         request_serializer=request_serializer,
         response_deserializer=response_deserializer)
     effective_metadata = _effective_metadata(metadata, metadata_transformer)
@@ -257,7 +254,7 @@ def _future_stream_unary(
     metadata_transformer, request_iterator, request_serializer,
     response_deserializer):
   multi_callable = channel.stream_unary(
-      _fully_qualified_method(group, method),
+      _common.fully_qualified_method(group, method),
       request_serializer=request_serializer,
       response_deserializer=response_deserializer)
   effective_metadata = _effective_metadata(metadata, metadata_transformer)
@@ -272,7 +269,7 @@ def _stream_stream(
     metadata_transformer, request_iterator, request_serializer,
     response_deserializer):
   multi_callable = channel.stream_stream(
-      _fully_qualified_method(group, method),
+      _common.fully_qualified_method(group, method),
       request_serializer=request_serializer,
       response_deserializer=response_deserializer)
   effective_metadata = _effective_metadata(metadata, metadata_transformer)
diff --git a/src/python/grpcio/grpc/beta/_server_adaptations.py b/src/python/grpcio/grpc/beta/_server_adaptations.py
index 52eadf2315..79e6ca87eb 100644
--- a/src/python/grpcio/grpc/beta/_server_adaptations.py
+++ b/src/python/grpcio/grpc/beta/_server_adaptations.py
@@ -33,6 +33,7 @@ import collections
 import threading
 
 import grpc
+from grpc import _common
 from grpc.beta import interfaces
 from grpc.framework.common import cardinality
 from grpc.framework.common import style
@@ -287,36 +288,43 @@ def _simple_method_handler(
           None, _adapt_stream_stream_event(implementation.stream_stream_event))
 
 
+def _flatten_method_pair_map(method_pair_map):
+  method_pair_map = method_pair_map or {}
+  flat_map = {}
+  for method_pair in method_pair_map:
+    method = _common.fully_qualified_method(method_pair[0], method_pair[1])
+    flat_map[method] = method_pair_map[method_pair]
+  return flat_map
+
+
 class _GenericRpcHandler(grpc.GenericRpcHandler):
 
   def __init__(
       self, method_implementations, multi_method_implementation,
       request_deserializers, response_serializers):
-    self._method_implementations = method_implementations
+    self._method_implementations = _flatten_method_pair_map(
+        method_implementations)
+    self._request_deserializers = _flatten_method_pair_map(
+        request_deserializers)
+    self._response_serializers = _flatten_method_pair_map(
+        response_serializers)
     self._multi_method_implementation = multi_method_implementation
-    self._request_deserializers = request_deserializers or {}
-    self._response_serializers = response_serializers or {}
 
   def service(self, handler_call_details):
-    try:
-      group_name, method_name = handler_call_details.method.split(b'/')[1:3]
-    except ValueError:
+    method_implementation = self._method_implementations.get(
+        handler_call_details.method)
+    if method_implementation is not None:
+      return _simple_method_handler(
+          method_implementation,
+          self._request_deserializers.get(handler_call_details.method),
+          self._response_serializers.get(handler_call_details.method))
+    elif self._multi_method_implementation is None:
       return None
     else:
-      method_implementation = self._method_implementations.get(
-          (group_name, method_name,))
-      if method_implementation is not None:
-        return _simple_method_handler(
-            method_implementation,
-            self._request_deserializers.get((group_name, method_name,)),
-            self._response_serializers.get((group_name, method_name,)))
-      elif self._multi_method_implementation is None:
+      try:
+        return None  #TODO(nathaniel): call the multimethod.
+      except face.NoSuchMethodError:
         return None
-      else:
-        try:
-          return None  #TODO(nathaniel): call the multimethod.
-        except face.NoSuchMethodError:
-          return None
 
 
 class _Server(interfaces.Server):
diff --git a/src/python/grpcio/tests/qps/benchmark_client.py b/src/python/grpcio/tests/qps/benchmark_client.py
index e2922347f9..1b100bb168 100644
--- a/src/python/grpcio/tests/qps/benchmark_client.py
+++ b/src/python/grpcio/tests/qps/benchmark_client.py
@@ -31,12 +31,9 @@
 
 import abc
 import time
-try:
-  import Queue as queue  # Python 2.x
-except ImportError:
-  import queue  # Python 3
 
 from concurrent import futures
+from six.moves import queue
 
 from grpc.beta import implementations
 from grpc.framework.interfaces.face import face
diff --git a/src/python/grpcio/tests/qps/client_runner.py b/src/python/grpcio/tests/qps/client_runner.py
index 2d1d981733..1fd58687ad 100644
--- a/src/python/grpcio/tests/qps/client_runner.py
+++ b/src/python/grpcio/tests/qps/client_runner.py
@@ -34,7 +34,7 @@ ClientRunner invokes either periodically or in response to some event.
 """
 
 import abc
-import thread
+import threading
 import time
 
 
@@ -61,15 +61,18 @@ class OpenLoopClientRunner(ClientRunner):
     super(OpenLoopClientRunner, self).__init__(client)
     self._is_running = False
     self._interval_generator = interval_generator
+    self._dispatch_thread = threading.Thread(
+        target=self._dispatch_requests, args=())
 
   def start(self):
     self._is_running = True
     self._client.start()
-    thread.start_new_thread(self._dispatch_requests, ())
-
+    self._dispatch_thread.start()
+   
   def stop(self):
     self._is_running = False
     self._client.stop()
+    self._dispatch_thread.join()
     self._client = None
 
   def _dispatch_requests(self):
diff --git a/src/python/grpcio/tests/stress/client.py b/src/python/grpcio/tests/stress/client.py
index e2e016760c..0de2532cd8 100644
--- a/src/python/grpcio/tests/stress/client.py
+++ b/src/python/grpcio/tests/stress/client.py
@@ -30,10 +30,10 @@
 """Entry point for running stress tests."""
 
 import argparse
-import Queue
 import threading
 
 from grpc.beta import implementations
+from six.moves import queue
 from src.proto.grpc.testing import metrics_pb2
 from src.proto.grpc.testing import test_pb2
 
@@ -94,7 +94,7 @@ def run_test(args):
   test_cases = _parse_weighted_test_cases(args.test_cases)
   test_servers = args.server_addresses.split(',')
   # Propagate any client exceptions with a queue
-  exception_queue = Queue.Queue()
+  exception_queue = queue.Queue()
   stop_event = threading.Event()
   hist = histogram.Histogram(1, 1)
   runners = []
@@ -121,7 +121,7 @@ def run_test(args):
     if timeout_secs < 0:
       timeout_secs = None
     raise exception_queue.get(block=True, timeout=timeout_secs)
-  except Queue.Empty:
+  except queue.Empty:
     # No exceptions thrown, success
     pass
   finally:
diff --git a/src/python/grpcio/tests/unit/_adapter/_intermediary_low_test.py b/src/python/grpcio/tests/unit/_adapter/_intermediary_low_test.py
index 22d4b019c7..09ebdeff33 100644
--- a/src/python/grpcio/tests/unit/_adapter/_intermediary_low_test.py
+++ b/src/python/grpcio/tests/unit/_adapter/_intermediary_low_test.py
@@ -164,15 +164,15 @@ class EchoTest(unittest.TestCase):
     self.assertIsNotNone(service_accepted)
     self.assertIs(service_accepted.kind, _low.Event.Kind.SERVICE_ACCEPTED)
     self.assertIs(service_accepted.tag, service_tag)
-    self.assertEqual(method, service_accepted.service_acceptance.method)
-    self.assertEqual(self.host, service_accepted.service_acceptance.host)
+    self.assertEqual(method.encode(), service_accepted.service_acceptance.method)
+    self.assertEqual(self.host.encode(), service_accepted.service_acceptance.host)
     self.assertIsNotNone(service_accepted.service_acceptance.call)
     metadata = dict(service_accepted.metadata)
-    self.assertIn(client_metadata_key, metadata)
-    self.assertEqual(client_metadata_value, metadata[client_metadata_key])
-    self.assertIn(client_binary_metadata_key, metadata)
+    self.assertIn(client_metadata_key.encode(), metadata)
+    self.assertEqual(client_metadata_value.encode(), metadata[client_metadata_key.encode()])
+    self.assertIn(client_binary_metadata_key.encode(), metadata)
     self.assertEqual(client_binary_metadata_value,
-                     metadata[client_binary_metadata_key])
+                     metadata[client_binary_metadata_key.encode()])
     server_call = service_accepted.service_acceptance.call
     server_call.accept(self.server_completion_queue, finish_tag)
     server_call.add_metadata(server_leading_metadata_key,
@@ -186,12 +186,12 @@ class EchoTest(unittest.TestCase):
     self.assertEqual(_low.Event.Kind.METADATA_ACCEPTED, metadata_accepted.kind)
     self.assertEqual(metadata_tag, metadata_accepted.tag)
     metadata = dict(metadata_accepted.metadata)
-    self.assertIn(server_leading_metadata_key, metadata)
-    self.assertEqual(server_leading_metadata_value,
-                     metadata[server_leading_metadata_key])
-    self.assertIn(server_leading_binary_metadata_key, metadata)
+    self.assertIn(server_leading_metadata_key.encode(), metadata)
+    self.assertEqual(server_leading_metadata_value.encode(),
+                     metadata[server_leading_metadata_key.encode()])
+    self.assertIn(server_leading_binary_metadata_key.encode(), metadata)
     self.assertEqual(server_leading_binary_metadata_value,
-                     metadata[server_leading_binary_metadata_key])
+                     metadata[server_leading_binary_metadata_key.encode()])
 
     for datum in test_data:
       client_call.write(datum, write_tag, _low.WriteFlags.WRITE_NO_COMPRESS)
@@ -277,17 +277,17 @@ class EchoTest(unittest.TestCase):
     self.assertIsNone(read_accepted.bytes)
     self.assertEqual(_low.Event.Kind.FINISH, finish_accepted.kind)
     self.assertEqual(finish_tag, finish_accepted.tag)
-    self.assertEqual(_low.Status(_low.Code.OK, details), finish_accepted.status)
+    self.assertEqual(_low.Status(_low.Code.OK, details.encode()), finish_accepted.status)
     metadata = dict(finish_accepted.metadata)
-    self.assertIn(server_trailing_metadata_key, metadata)
-    self.assertEqual(server_trailing_metadata_value,
-                     metadata[server_trailing_metadata_key])
-    self.assertIn(server_trailing_binary_metadata_key, metadata)
+    self.assertIn(server_trailing_metadata_key.encode(), metadata)
+    self.assertEqual(server_trailing_metadata_value.encode(),
+                     metadata[server_trailing_metadata_key.encode()])
+    self.assertIn(server_trailing_binary_metadata_key.encode(), metadata)
     self.assertEqual(server_trailing_binary_metadata_value,
-                     metadata[server_trailing_binary_metadata_key])
+                     metadata[server_trailing_binary_metadata_key.encode()])
     self.assertSetEqual(set(key for key, _ in finish_accepted.metadata),
-                        set((server_trailing_metadata_key,
-                             server_trailing_binary_metadata_key,)))
+                        set((server_trailing_metadata_key.encode(),
+                             server_trailing_binary_metadata_key.encode(),)))
 
     self.assertSequenceEqual(test_data, server_data)
     self.assertSequenceEqual(test_data, client_data)
@@ -302,7 +302,8 @@ class EchoTest(unittest.TestCase):
     self._perform_echo_test([_BYTE_SEQUENCE])
 
   def testManyOneByteEchoes(self):
-    self._perform_echo_test(_BYTE_SEQUENCE)
+    self._perform_echo_test(
+        [_BYTE_SEQUENCE[i:i+1] for i in range(len(_BYTE_SEQUENCE))])
 
   def testManyManyByteEchoes(self):
     self._perform_echo_test(_BYTE_SEQUENCE_SEQUENCE)
@@ -409,7 +410,7 @@ class CancellationTest(unittest.TestCase):
 
     finish_event = self.client_events.get()
     self.assertEqual(_low.Event.Kind.FINISH, finish_event.kind)
-    self.assertEqual(_low.Status(_low.Code.CANCELLED, 'Cancelled'),
+    self.assertEqual(_low.Status(_low.Code.CANCELLED, b'Cancelled'),
                                  finish_event.status)
 
     self.assertSequenceEqual(test_data, server_data)
diff --git a/src/python/grpcio/tests/unit/_adapter/_low_test.py b/src/python/grpcio/tests/unit/_adapter/_low_test.py
index ec46617996..e09a1f2564 100644
--- a/src/python/grpcio/tests/unit/_adapter/_low_test.py
+++ b/src/python/grpcio/tests/unit/_adapter/_low_test.py
@@ -148,11 +148,11 @@ class InsecureServerInsecureClient(unittest.TestCase):
     # Check that Python's user agent string is a part of the full user agent
     # string
     received_initial_metadata_dict = dict(received_initial_metadata)
-    self.assertIn('user-agent', received_initial_metadata_dict)
-    self.assertIn('Python-gRPC-{}'.format(_grpcio_metadata.__version__),
-                  received_initial_metadata_dict['user-agent'])
-    self.assertEqual(method, request_event.call_details.method)
-    self.assertEqual(host, request_event.call_details.host)
+    self.assertIn(b'user-agent', received_initial_metadata_dict)
+    self.assertIn('Python-gRPC-{}'.format(_grpcio_metadata.__version__).encode(),
+                  received_initial_metadata_dict[b'user-agent'])
+    self.assertEqual(method.encode(), request_event.call_details.method)
+    self.assertEqual(host.encode(), request_event.call_details.host)
     self.assertLess(abs(deadline - request_event.call_details.deadline),
                     deadline_tolerance)
 
@@ -198,12 +198,12 @@ class InsecureServerInsecureClient(unittest.TestCase):
             test_common.metadata_transmitted(server_initial_metadata,
                                              client_result.initial_metadata))
       elif client_result.type == _types.OpType.RECV_MESSAGE:
-        self.assertEqual(response, client_result.message)
+        self.assertEqual(response.encode(), client_result.message)
       elif client_result.type == _types.OpType.RECV_STATUS_ON_CLIENT:
         self.assertTrue(
             test_common.metadata_transmitted(server_trailing_metadata,
                                              client_result.trailing_metadata))
-        self.assertEqual(server_status_details, client_result.status.details)
+        self.assertEqual(server_status_details.encode(), client_result.status.details)
         self.assertEqual(server_status_code, client_result.status.code)
     self.assertEqual(set([
           _types.OpType.SEND_INITIAL_METADATA,
@@ -220,7 +220,7 @@ class InsecureServerInsecureClient(unittest.TestCase):
       self.assertNotIn(client_result.type, found_server_op_types)
       found_server_op_types.add(server_result.type)
       if server_result.type == _types.OpType.RECV_MESSAGE:
-        self.assertEqual(request, server_result.message)
+        self.assertEqual(request.encode(), server_result.message)
       elif server_result.type == _types.OpType.RECV_CLOSE_ON_SERVER:
         self.assertFalse(server_result.cancelled)
     self.assertEqual(set([
diff --git a/src/python/grpcio/tests/unit/_cython/cygrpc_test.py b/src/python/grpcio/tests/unit/_cython/cygrpc_test.py
index 4039c1b99b..a006a20ce3 100644
--- a/src/python/grpcio/tests/unit/_cython/cygrpc_test.py
+++ b/src/python/grpcio/tests/unit/_cython/cygrpc_test.py
@@ -37,7 +37,7 @@ from tests.unit import test_common
 from tests.unit import resources
 
 
-_SSL_HOST_OVERRIDE = 'foo.test.google.fr'
+_SSL_HOST_OVERRIDE = b'foo.test.google.fr'
 _CALL_CREDENTIALS_METADATA_KEY = 'call-creds-key'
 _CALL_CREDENTIALS_METADATA_VALUE = 'call-creds-value'
 _EMPTY_FLAGS = 0
diff --git a/src/python/grpcio/tests/unit/_links/_transmission_test.py b/src/python/grpcio/tests/unit/_links/_transmission_test.py
index 888684d197..1f6edd18ca 100644
--- a/src/python/grpcio/tests/unit/_links/_transmission_test.py
+++ b/src/python/grpcio/tests/unit/_links/_transmission_test.py
@@ -153,7 +153,7 @@ class RoundTripTest(unittest.TestCase):
         invocation_mate.tickets()[-1].termination,
         links.Ticket.Termination.COMPLETION)
     self.assertIs(invocation_mate.tickets()[-1].code, test_code)
-    self.assertEqual(invocation_mate.tickets()[-1].message, test_message)
+    self.assertEqual(invocation_mate.tickets()[-1].message, test_message.encode())
 
   def _perform_scenario_test(self, scenario):
     test_operation_id = object()
diff --git a/src/python/grpcio/tests/unit/_rpc_test.py b/src/python/grpcio/tests/unit/_rpc_test.py
index 1c7a14c5d0..b33bff490c 100644
--- a/src/python/grpcio/tests/unit/_rpc_test.py
+++ b/src/python/grpcio/tests/unit/_rpc_test.py
@@ -29,6 +29,8 @@
 
 """Test of gRPC Python's application-layer API."""
 
+from __future__ import division
+
 import itertools
 import threading
 import unittest
@@ -41,9 +43,9 @@ from tests.unit.framework.common import test_constants
 from tests.unit.framework.common import test_control
 
 _SERIALIZE_REQUEST = lambda bytestring: bytestring * 2
-_DESERIALIZE_REQUEST = lambda bytestring: bytestring[len(bytestring) / 2:]
+_DESERIALIZE_REQUEST = lambda bytestring: bytestring[len(bytestring) // 2:]
 _SERIALIZE_RESPONSE = lambda bytestring: bytestring * 3
-_DESERIALIZE_RESPONSE = lambda bytestring: bytestring[:len(bytestring) / 3]
+_DESERIALIZE_RESPONSE = lambda bytestring: bytestring[:len(bytestring) // 3]
 
 _UNARY_UNARY = b'/test/UnaryUnary'
 _UNARY_STREAM = b'/test/UnaryStream'
@@ -189,7 +191,7 @@ class RPCTest(unittest.TestCase):
     self._server.add_generic_rpc_handlers((_GenericHandler(self._handler),))
     self._server.start()
 
-    self._channel = grpc.insecure_channel(b'localhost:%d' % port)
+    self._channel = grpc.insecure_channel('localhost:%d' % port)
 
   # TODO(nathaniel): Why is this necessary, and only in some development
   # environments?
diff --git a/src/python/grpcio/tests/unit/beta/_beta_features_test.py b/src/python/grpcio/tests/unit/beta/_beta_features_test.py
index bb2893a21b..3a9701b8eb 100644
--- a/src/python/grpcio/tests/unit/beta/_beta_features_test.py
+++ b/src/python/grpcio/tests/unit/beta/_beta_features_test.py
@@ -42,8 +42,8 @@ from tests.unit.framework.common import test_constants
 
 _SERVER_HOST_OVERRIDE = 'foo.test.google.fr'
 
-_PER_RPC_CREDENTIALS_METADATA_KEY = 'my-call-credentials-metadata-key'
-_PER_RPC_CREDENTIALS_METADATA_VALUE = 'my-call-credentials-metadata-value'
+_PER_RPC_CREDENTIALS_METADATA_KEY = b'my-call-credentials-metadata-key'
+_PER_RPC_CREDENTIALS_METADATA_VALUE = b'my-call-credentials-metadata-value'
 
 _GROUP = 'group'
 _UNARY_UNARY = 'unary-unary'
diff --git a/src/python/grpcio/tests/unit/beta/_not_found_test.py b/src/python/grpcio/tests/unit/beta/_not_found_test.py
index 44fcd1e13c..37b8c49120 100644
--- a/src/python/grpcio/tests/unit/beta/_not_found_test.py
+++ b/src/python/grpcio/tests/unit/beta/_not_found_test.py
@@ -61,7 +61,7 @@ class NotFoundTest(unittest.TestCase):
 
   def test_future_stream_unary_not_found(self):
     rpc_future = self._generic_stub.future_stream_unary(
-        'grupe', 'mevvod', b'def', test_constants.LONG_TIMEOUT)
+        'grupe', 'mevvod', [b'def'], test_constants.LONG_TIMEOUT)
     with self.assertRaises(face.LocalError) as exception_assertion_context:
       rpc_future.result()
     self.assertIs(
diff --git a/src/python/grpcio/tests/unit/framework/interfaces/base/test_cases.py b/src/python/grpcio/tests/unit/framework/interfaces/base/test_cases.py
index 4f8e26c9a2..5d16bf98be 100644
--- a/src/python/grpcio/tests/unit/framework/interfaces/base/test_cases.py
+++ b/src/python/grpcio/tests/unit/framework/interfaces/base/test_cases.py
@@ -29,6 +29,8 @@
 
 """Tests of the base interface of RPC Framework."""
 
+from __future__ import division
+
 import logging
 import random
 import threading
@@ -54,13 +56,13 @@ class _Serialization(test_interfaces.Serialization):
     return request + request
 
   def deserialize_request(self, serialized_request):
-    return serialized_request[:len(serialized_request) / 2]
+    return serialized_request[:len(serialized_request) // 2]
 
   def serialize_response(self, response):
     return response * 3
 
   def deserialize_response(self, serialized_response):
-    return serialized_response[2 * len(serialized_response) / 3:]
+    return serialized_response[2 * len(serialized_response) // 3:]
 
 
 def _advance(quadruples, operator, controller):
diff --git a/src/python/grpcio/tests/unit/test_common.py b/src/python/grpcio/tests/unit/test_common.py
index 7b4d20dccb..b779f65e7e 100644
--- a/src/python/grpcio/tests/unit/test_common.py
+++ b/src/python/grpcio/tests/unit/test_common.py
@@ -61,6 +61,10 @@ def metadata_transmitted(original_metadata, transmitted_metadata):
   original = collections.defaultdict(list)
   for key_value_pair in original_metadata:
     key, value = tuple(key_value_pair)
+    if not isinstance(key, bytes):
+      key = key.encode()
+    if not isinstance(value, bytes):
+      value = value.encode()
     original[key].append(value)
   transmitted = collections.defaultdict(list)
   for key_value_pair in transmitted_metadata: