process csv in matplotlib

import csvfrom matplotlib import pyplot as pltfrom datetime import datetimefilename = 'death_valley_2014.csv'with open(filename) as f:    reader = csv.reader(f)    header_row = next(reader)    dates,highs,lows=[],[],[]    for row in reader:        try:            current_date=datetime.strptime(row[0],'%Y-%m-%d')            high = int(row[1])            low = int(row[3])        except ValueError:            print(current_date,'missing data')        else:            lows.append(low)            highs.append(high)            dates.append(current_date)    fig = plt.figure(dpi=128,figsize=(10,6))    #alpha assign the transparency    plt.plot(dates,highs,c='red',alpha=0.5)    plt.plot(dates,lows,c='blue',alpha=0.5)    plt.fill_between(dates,highs,lows,facecolor='blue',alpha=0.1)    plt.title("Daily high and low temperature, 2014",fontsize = 24)    plt.xlabel("",fontsize =16)    #avoid to be covered    fig.autofmt_xdate()    plt.ylabel('Temperature(F)',fontsize = 16)    plt.tick_params(axis='both',which='major',labelsize = 16)    plt.show()