def eval_from_json(json):
        """ Evaluates OBV from JSON (typically Poloniex API response)

        Args:
            json: List of dates where each entry is a dict of raw market data.

        Returns:
            Float of OBV
        """
        closes = poloniex.get_attribute(json, 'close')
        volumes = poloniex.get_attribute(json, 'volume')
        obv = 0
        for date in range(1, len(json)):
            curr = {'close': closes[date], 'volume': volumes[date]}
            prev = {'close': closes[date - 1], 'obv': obv}
            obv = OBV.eval_algorithm(curr, prev)
        return obv