ms.py

stocks = [(24, '2014-01-02'),
          (23, '2014-01-03'),
          (22, '2014-01-04'),
          (26, '2014-01-05'),
          (19, '2014-01-06'),
          (20, '2014-01-08'),
          (25, '2014-01-09'),
          (24, '2014-01-10')]


def big_drop(s):
    """
    Assumes s to be a non empty array of tuples
    """
    assert len(s) > 0

    last_peak = s[0]
    biggest_drop = 0
    for stock in s:
        print("last peak: %s, biggest drop: %s" % (last_peak, biggest_drop))
        last_peak_price = last_peak[0]
        price = stock[0]

        if last_peak_price >= price:
            drop = last_peak_price - price
            if drop > biggest_drop:
                biggest_drop = drop
        else:
            last_peak = stock
           
       
    return biggest_drop

if __name__ == '__main__':
    b = big_drop(stocks)
    print("The biggest price drop is: %s" % b)