python 实现FTP功能问题求帮助

import ftplib
ftp=ftplib.FTP()
IP_ADDRESS='172.25.127.164'
port=21
username="ss"
password="ss"
ftp.connect(IP_ADDRESS, port)
ftp.login(username, password)
print ftp.getwelcome()
currentpath='/ss/log'
ftp.cwd(currentpath)
ftp.dir()
bufsize=1024
DownLocalFilename='zx.log'
file_handle=open(DownLocalFilename,'wb').write
ftp.retrbinary('RETR DownLocalFilename',file_handle,bufsize)
ftp.close()
报错如下：
Traceback (most recent call last):
File "ftp.py", line 16, in <module>
ftp.retrbinary('RETR DownLocalFilename',file_handle,bufsize)
File "C:\Python27\lib\ftplib.py", line 414, in retrbinary
conn = self.transfercmd(cmd, rest)
File "C:\Python27\lib\ftplib.py", line 376, in transfercmd
return self.ntransfercmd(cmd, rest)[0]
File "C:\Python27\lib\ftplib.py", line 339, in ntransfercmd
resp = self.sendcmd(cmd)
File "C:\Python27\lib\ftplib.py", line 249, in sendcmd
return self.getresp()
File "C:\Python27\lib\ftplib.py", line 224, in getresp
raise error_perm, resp
ftplib.error_perm: 550 DownLocalFilename: A file or directory in the path name d
oes not exist.