def k_day_percent_change(k, df):
    """
    Computes the k-day adjusted close percent change.
    Example: k=2, is the daily percent change

    Arguments:
    k --  number of days into past to use , k>1
    df -- yahoo finance dataframe. Must be indexed by data, and have columne adj_close
    """
    return (df.open / df.adj_close.shift(k)) - 1