Boto: upload para o Amazon S3 OK, mas faça o upload para o Google Cloud Storage: 'str' não suporta a interface do buffer - amazon-s3, google-cloud-storage, boto

Estou usando códigos quase exatos para fazer upload de arquivos para Amazon S3 e Google Cloud Storage, respectivamente, usando boto:

import boto

filename = "abc.png"
filenameWithPath = os.path.dirname(os.path.realpath(__file__)) + "/" + filename
cloudFilename = "uploads/" + filename

# Upload to Amazon S3
conn = boto.connect_s3(aws_access_key_id=AWS_ACCESS_KEY, aws_secret_access_key=AWS_SECRET_KEY)
bucket = conn.get_bucket(AWS_BUCKET_NAME)
fpic = boto.s3.key.Key(bucket)
fpic.key = cloudFilename
fpic.set_contents_from_filename(filenameWithPath)

# Upload to Google Cloud Storage
conn = boto.connect_gs(gs_access_key_id=GS_ACCESS_KEY, gs_secret_access_key=GS_SECRET_KEY)
bucket = conn.get_bucket(GS_BUCKET_NAME)
fpic = boto.s3.key.Key(bucket)
fpic.key = cloudFilename
fpic.set_contents_from_filename(filenameWithPath)

A parte do código do Amazon S3 funciona perfeitamente. No entanto, a parte do Google Cloud Storage fornece a mensagem de erro TypeError, "str" does not support the buffer interface na declaração fpic.set_contents_from_filename(...).

Qual era o problema?

Respostas:

Request Method: POST
Request URL: http://localhost:8000/upload/

Traceback:
File "<folder of virtual environ>/lib/python3.4/site-packages/django/core/handlers/base.py" in get_response
132.                     response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "<folder of my project>/upload/views.py" in upload
59.         fpic.set_contents_from_filename(filenameWithPath)
File "<folder of virtual environ>/lib/python3.4/site-packages/boto/s3/key.py" in set_contents_from_filename
1362.                                                encrypt_key=encrypt_key)
File "<folder of virtual environ>/lib/python3.4/site-packages/boto/s3/key.py" in set_contents_from_file
1293.                            chunked_transfer=chunked_transfer, size=size)
File "<folder of virtual environ>/lib/python3.4/site-packages/boto/s3/key.py" in send_file
750.                                  chunked_transfer=chunked_transfer, size=size)
File "<folder of virtual environ>/lib/python3.4/site-packages/boto/s3/key.py" in _send_file_internal
951.             query_args=query_args
File "<folder of virtual environ>/lib/python3.4/site-packages/boto/s3/connection.py" in make_request
664.             retry_handler=retry_handler
File "<folder of virtual environ>/lib/python3.4/site-packages/boto/connection.py" in make_request
1071.                           retry_handler=retry_handler)
File "<folder of virtual environ>/lib/python3.4/site-packages/boto/connection.py" in _mexe
940.                                       request.body, request.headers)
File "<folder of virtual environ>/lib/python3.4/site-packages/boto/s3/key.py" in sender
840.                     http_conn.send("%x;rn" % chunk_len)
File "/usr/lib/python3.4/http/client.py" in send
876.                     self.sock.sendall(d)
File "/usr/lib/python3.4/ssl.py" in sendall
718.                 v = self.send(data[count:])
File "/usr/lib/python3.4/ssl.py" in send
679.                 v = self._sslobj.write(data)

Exception Type: TypeError at /upload/
Exception Value: "str" does not support the buffer interface