python解决：不能将字符串转为float类型

sunday=mysql.sql("select LJJZ from data LIMIT 1")
monday=mysql.sql("select LJJZ from data LIMIT 7,1")

print(sunday)#从数据库中取数据，得到[["2.1537"]]
print(monday)#从数据库中取数据，得到[["2.1887"]]
list_monday = sunday.replace('[','').replace(']','')#去掉中括号
print(list_monday,type(list_monday))#输出"2.1537" 
list_monday_1=eval(list_monday)#去掉双引号
list_monday_2=list_monday_1.strip().split()#去掉字符串中其他字符
print(list_monday_2)#输出['2.1537']
#实现列表转为float
list2=''
for i in list_monday_2:
    list2=list2+str(i)
print(float(list2))
f_list=float(list2)
print(f_list,type(f_list))