ax= plt.subplot()
mondays = WeekdayLocator(MONDAY)
mondays
weekFormatter = DateFormatter('%y %b %d')
ax.xaxis.set_major_locator(mondays)
ax.xaxis.set_minor_locator(DayLocator() )
ax.xaxis.set_major_formatter(weekFormatter)
plt.rcParams['font.sans-serif'] = ['SimHei']
plt.rcParams['axes.unicode_minus'] = False
ax.set_title("妙可蓝多2020年K线图")
candlestick_ohlc(ax, MKLD5, width=0.7,colorup='r', colordown='g')
plt.setp(plt.gca().get_xticklabels(),rotation=50, horizontalalignment='center')
plt.show()


TypeError: unsupported operand type(s) for -: 'str' and 'str'
我再运行代码的时候出现了这种错误，该怎么解决