Upload data group file list with Python Bigsuds iControl

Hello,

Short version: What is the correct way to upload an external data group file using the python bigsuds API ?

Long version:

I am trying to use python and bigsuds to create Data Groups based on external files.

I managed to create the data group using the following method:

b.LocalLB.Class.create_external_class_v2(["datagroup_name_test"],["file_name_test"])

It works but the file_name_test must be already there, uploaded before via web interface. I created a file dg.txt with the following content:

"name1" := "value1",
"name2" := "value2",
"name3" := "value3",

And I wrote the following function to upload it:

def uploadfile(bigip,filename):
    fileobj = open(filename,'r')
    DF_CHUNK_SIZE = 1024
    done = False
    first = True
    while not done:
        text = base64.b64encode(fileobj.read(DF_CHUNK_SIZE))

        if first:
            chain_type = 'FILE_FIRST'
            first = False
        else:
            if len(text) < DF_CHUNK_SIZE:
                chain_type = 'FILE_LAST'
                done = True
            else:
                chain_type = 'FILE_MIDDLE'

        bigip.System.ConfigSync.upload_file(file_name="/config/filestore/files_d/Common_d/data_group_d/"+filename,file_context=dict(file_data=text,chain_type=chain_type))

I cant upload the file, I get this error:

ServerError: Server raised fault: 'Exception caught in  System::urn:iControl:System/ConfigSync::upload_file()
Exception: Common::OperationFailed
    primary_error_code   : 16908289 (0x01020001)
    secondary_error_code : 0
    error_string         : Error opening file for write operations'

I feel I am doing it in the wrong way. What is the correct way to upload an external data group file using the python bigsuds API ?