problems with python RPC

Hi,

I am new to avro and I am trying to use it for RPC calls from Python to
Python.

I follow the same structure shown in
https://github.com/phunt/avro-rpc-quickstart/blob/master/src/main/python/

When my message returns just a string, everything works fine.
However, when it should return a list of a complex type, it gives me a
weird exception with no clue of where the error could be. I used the exact
same structure shown in the github project above.

What could I do to get more info about the error? Any clue of what could I
be doing wrong?

My code
def invoke(self, msg, req):
result = []
return (result)

The exception:
Traceback (most recent call last):
File "./client.py", line 47, in <module>
result = perform_call("list_categories", params)
File "./client.py", line 33, in perform_call
result = requestor.request(message, args)
File "/home/mvalle/pyve01/local/lib/python2.7/site-packages/avro/ipc.py",
line 145, in request
return self.issue_request(call_request, message_name, request_datum)
File "/home/mvalle/pyve01/local/lib/python2.7/site-packages/avro/ipc.py",
line 262, in issue_request
return self.read_call_response(message_name, buffer_decoder)
File "/home/mvalle/pyve01/local/lib/python2.7/site-packages/avro/ipc.py",
line 238, in read_call_response
return self.read_response(writers_schema, readers_schema, decoder)
File "/home/mvalle/pyve01/local/lib/python2.7/site-packages/avro/ipc.py",
line 246, in read_response
result = datum_reader.read(decoder)
File "/home/mvalle/pyve01/local/lib/python2.7/site-packages/avro/io.py",
line 445, in read
return self.read_data(self.writers_schema, self.readers_schema, decoder)
File "/home/mvalle/pyve01/local/lib/python2.7/site-packages/avro/io.py",
line 488, in read_data
return self.read_union(writers_schema, readers_schema, decoder)
File "/home/mvalle/pyve01/local/lib/python2.7/site-packages/avro/io.py",
line 646, in read_union
index_of_schema = int(decoder.read_long())
File "/home/mvalle/pyve01/local/lib/python2.7/site-packages/avro/io.py",
line 184, in read_long
b = ord(self.read(1))
TypeError: ord() expected a character, but string of length 0 found

My protocol definition:

"protocol":"s1mbi0se",
"namespace":"modules.service_bus",
"messages":{
"list_categories":{
"request":[

"type":"string",
"name":"prefix"
},

"type":"string",
"name":"type"

],
"response":[

"type":"Category",
"name":"category"

},
"types":[

"fields":[

"type":"string",
"name":"tos"
},

"type":"string",
"name":"froms"
},

"type":"string",
"name":"bodys"

],
"type":"record",
"name":"Category"

Best regards,