Getting a bag out of a python stream

[Sal Uryasev]

What would be the right syntax to stream through a python script?

This does not seem to work, as pig complains about the syntax:
DEFINE force_layout `ForceDirected.py`
  SHIP ('$python_dir/ForceDirected.py');
layout = STREAM connection_info THROUGH force_layout
  AS (user_id:chararray, nodes:bag{t:tuple(x:int, y:int, created:int)}, 
edges:bag{t:tuple(source:int, destination:int)});


[java] 10/10/11 18:55:05 ERROR python_script_runner: 2010-10-11 18:55:05,729 
[main] ERROR org.apache.pig.tools.grunt.Grunt - ERROR 1000: Error during 
parsing. Encountered " <PATH> "user_id, "" at line 7, column 1.


Thanks for your help!

-Sal Uryasev