我找到了错误的原因，但我不知道如何解决

'wb'表中没有A2数据，即来自'客户代码'的数据，报此错误。

我正在处理XLSX表，分析数据，并根据样本重新分配存储的数据。根据样本表的分析，现在处理的表没有样本数据。在这种情况下，我不处理它们，而只存储现有数据。

#!/usr/bin/env python
#-*- coding: utf-8 -*-

import openpyxl 

wb = openpyxl.load_workbook('康之源药业.xlsx')
s1 = wb.active

def getdata(filename):
    data = []
    for col in s1.columns:
        '''取出每一列的值'''
        line = [cell.value for cell in col if cell.value != None]
        data.append(line)
    return data


def cachedata(data):
    '''数据储存'''
    for i in data:
        '''为空的列表不处理'''
        if len(i) != 0:
            #data.remove(i)
            if i[0] == '销售时间':
                a0 = i
            if i[0] == '生产厂家':
                a1 = i
            if i[0] == '客户代码':
                a2 = i 
            if i[0] == '客户名称':
                a3 = i
            if i[0] == '产品代码':
                a4 = i
            if i[0] == '产品名称':
                a5 = i
            if i[0] == '产品规格':
                a6 = i
            if i[0] == '单位':
                a7 = i
            if i[0] == '批号':
                a8 = i
            if i[0] == '数量':
                a9 = i
            if i[0] == '含税单价':
                a10 = i
            if i[0] == '商品名称':
                a11 = i
            if i[0] == '不含税单价':
                a12 = i
            if i[0] == '含税金额':
                a13 = i
            if i[0] == '不含税金额':
                a14 = i
            if i[0] == '出货类型':
                a15 = i
            if i[0] == '客户城市':
                a16 = i
            if i[0] == '客户地址':
                a17 = i
            if i[0] == '经销商发货单号':
                a18 = i
            if i[0] == '出货仓库':
                a19 = i
            if i[0] == '购进单位编码':
                a20 = i
            if i[0] == '一级商编码':
                a21 = i
            if i[0] == '一级商名称':
                a22 = i
    return a0,a1,a2,a3,a4,a5,a6,a7,a8,a9,a10,a11,a12,a13,a14,a15,a16,a17,a18,a19,a20,a21,a22

if __name__ == '__main__':
    data = getdata(wb)
    cachedata = cachedata(data)
    a2 = cachedata[2]
    print(a2)

错误信息：

Traceback (most recent call last):
  File "C:\Users\Yang\Desktop\3.py", line 107, in <module>
    cachedata = cachedata(data)
  File "C:\Users\Yang\Desktop\3.py", line 76, in cachedata
    return a0,a1,a2,a3,a4,a5,a6,a7,a8,a9,a10,a11,a12,a13,a14,a15,a16,a17,a18,a19,a20,a21,a22
UnboundLocalError: local variable 'a2' referenced before assignment

但是当我添加a2数据时，代码有效。