f = open('作业一附加选做题素材.txt',encoding='utf-8')
txt = f.read()
f.close()
txt

剔除页脚内容

index = txt.find('\n顺丰控股股份有限公司')
txt_target = txt[:index]
txt_target

通过句号判断最后一个句子

e = txt_target.rfind('。')
s = txt_target[:e].rfind('。')
last = txt_target[s+1:e+1]
last = last.replace('\n','')

print(len(last))