Python ‘NoneType‘ object has no attribute ‘split‘

大佬们,我今天尝试openpyxl的时候报错'NoneType' object has no attribute 'split',百度搜索了一下看不懂,可以帮忙解释一下么?

#---------------------------------------------------------------
form openpyxl import load_workbook
wb = load_workbook("C:\MJP\6_CODE\a.xlsx")
sheet1 = wb.active
b = []
sepp = 1
for i in sheet1["e"]
    list = i.value.split('/')
    for k in range(1,len(list1)+1):
        valuea = sheet1.cell(row=i.row,column=3).value
        valueb = list1[k-1]
    print(sepp,valuea,sep='t')
    sepp+=1
#---------------------------------------------------------------