Python处理DataFrame的问题

[shuailiuyia]

sql='SELECT id,sid,storename,sid_union FROM `stores'
df = pd.read_sql(sql,connection,index_col="id")

length=df.iloc[:,0].size
#print(type(df))
#cursor.execute(sql)
#print(df['sid_union'][1])
for i in range(10,length+1):
    if df['sid_union'][i]==None:
        df['sid_union'][i]=df['sid'][i]
        for j in range(i+1,length+1):
            if df['storename'][j]==df['storename'][i]:
                df['sid_union'][j]=df['sid'][i]

    else:
        continue
print(df)

报这样的错误