If you are considering to add new methods in Python to use them in RPC from JavaScript, then consider the following options of method decorators: if you've to deal with ids/recordsets then for python method definition choose decorator:
Or if it's simple function that does not have to deal with records/ids then for python method choose decorator:
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(empty array) as first argument in javascript...
References: Odoo RPC documentation, Odoo 8 API method decorators