Python astype(np.float)函数使用方法解析

import pymysql
import numpy as np

conn = pymysql.connect(host='39.106.168.84', user='xxxxxx', password='xxxxxx', port=3306,
            db='flask_topvj_net')
cur = conn.cursor()
sql = "SELECT `name`, `age`,`nr` FROM `student` WHERE 1"
cur.execute(sql)
u = cur.fetchall()
u=np.array(u)
conn.close()
print(u)

#a=u[:,1]*5
#b=u[:,2]*5#错误示范

a=u[:,1].astype(np.float)*5
b=u[:,2].astype(np.float)*5
print(a)
print(b)