请教这种类似时间持续的演变图如何实现

qxsw2016

想要的结果如图，横轴年，纵轴表示出入梅（梅雨期）。我想了个思路，就是用bar实现，至做了几步，就不知道怎么搞了，请老师帮忙看看。脚本如下：
t_str = '2012-03-05'
startDate = ['2011-03-05','2012-03-22','2013-04-01','2014-03-03',
             '2015-04-05','2016-02-28','2017-05-01','2018-03-23']
endDate = ['2011-07-08','2012-06-28','2013-07-07','2014-06-06',
           '2015-06-25','2016-07-25','2017-08-01','2018-08-21']
d = datetime.datetime.strptime(startDate[0], '%Y-%m-%d')
print endDate[0]
span = []
daten = len(startDate)
for i in range(daten):
    delta = datetime.datetime.strptime(endDate, '%Y-%m-%d')-datetime.datetime.strptime(startDate, '%Y-%m-%d')
    #print delta.days
    span.append(delta.days)
years = []
for i in range(2011, 2019):
    years.append(i)
yearn = len(years)
bar(years,span)
xlim(2011, 2018)
ylim(0,365)

pilgram

这个用boxplot就可以吧