python control excel by openpyxl, why use the '_'

I use openpyxl for my school Excel Code is:

import openpyxl
import random

workbook = openpyxl.Workbook()  #创建工作簿
worksheet = workbook.active  #打开活动Sheet（0）
for row in range(1,55): #54行
    for column in range(1,16): #15列
        randomValue = random.choice([36.1,36.2,36.3,36.4,36.5,36.6,36.7,36.8,36.9]) #随机选择范围内数
        #随机生成一个数
        _ = worksheet.cell(row=row, column=column, value="{0}".format(randomValue)) #传入随机数值
        #填入单元格
        print(row,column,randomValue) #反馈当前进度
workbook.save("初二11班.xlsx") #保存

I am tired of that '', why use it? 为什么要用 ‘’？ 它有什么作用？我无法理解