This decorator is intended to simplify error handling in request cycles with many callbacks. The idea is to decorate a callback function that takes its main "data" as a first positional argument, and a callback as a kwarg called "callback". The decorator will inspect the data argument and attempt to determine if it is an error (either a tornado…

passthrough_errors.py

def passthrough_errors(method):
    @functools.wraps(method)
    def wrapper(*args, **kwargs):
        callback = kwargs['callback']
        data = args[0]

        # Check if an error is being passed in, somehow
        error = None
        if isinstance(data, tornado.httpclient.HTTPResponse) and data.error:
            error = data.error
        elif isinstance(data, Exception):
            error = data
        # Short-circuit to the callback if there was an error
        if error:
            return callback(error)
        # try calling the function, and short-circuit on error
        try:
            method(*args, **kwargs)
        except Exception, e:
            return callback(e)
    return wrapper