import pandas as pd


def add_rec_bars(ax, dates=None):
    if dates is None:
        dates = pd.read_csv('/Users/tom/bin/rec_dates.csv',
                            parse_dates=['Peak', 'Trough'])
    for row in dates.iterrows():
        x = row[1]
        y1, y2 = ax.get_ylim()
        ax.fill_between(x, y1=y1, y2=y2, alpha=.25, color='k')
    return ax