python 操作mysql数据中fetchall()方式操作多次时返回数据为空

运行下面代码

from sqlalchemy import create_engine

engine = create_engine('mysql+pymysql://root:xxx@xxx:3306/xxx')
conn=engine.connect()
ss='1000324'
#result=conn.execute("select max(FDate) from big_V_fund_info where FCode=%s"%(ss))
result=conn.execute("select distinct FCode from big_V_info")
lis=result.fetchall()
print(len(result.fetchall()))
print(lis)
print(result.rowcount)
print(result.fetchall())
print(result.rowcount)
print(result.fetchall())

结果为：

0
[('10003624',), ('10005141',), ('10007217',), ('10010985',), ('10015297',), ('10015848',), ('10017235',), ('10024197',), ('10041805',), ('10046573',), ('10073527',), ('10074390',), ('10077446',), ('10142058',), ('10148047',), ('10280116',)]
16
[]
16
[]

说明：result.fetchall()运行一次之后，若再次运行会返回空值；所以需要先将其保存至一个变量中！