Utility function that can be used within the parse() implementation of
        sub classes to split a list of example into two lists for training and
        testing.

def split(examples, ratio=0.8):
        """
        Utility function that can be used within the parse() implementation of
        sub classes to split a list of example into two lists for training and
        testing.
        """
        split = int(ratio * len(examples))
        return examples[:split], examples[split:]