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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_arg(context, index):
 """get value from arg stream in async way"""

    if index < len(context.argstreams):
        arg = ""
        chunk = yield context.argstreams[index].read()
        while chunk:
            arg += chunk
            chunk = yield context.argstreams[index].read()

        raise tornado.gen.Return(arg)
    else:
        raise TChannelError()