def stock_price_at_date(lookup_date, ticker, lag=0):
    '''
    Returns the daily share price of a stock for a specified date range.

    Parameters
    ----------
    lookup_date : Datetime.datetime.date
         End date.
    ticker: str
        str corresponding the the stock's ticker symbol.
    lag : int
        length of trading days before start date

    Returns
    --------
    DataFrame :
        A stock's prices over a the given period.
    '''
    start = (timedelta(days=lag) - lookup_date)
    return DataReader(ticker, start=start, end=lookup_date,
                      data_source='yahoo').ix[0, 5]
dataset/ETHPy150Open agconti/KaggleAux/kaggleaux/utils.py/stock_price_at_date/swapped operands of `-`