Python错误：NameError：未定义全局名称“ ftp”

Question

I'm having an issue with trying to declare a global ftp object. I want the ftp connection to be check at certain times and refreshed or reconnected. I'm trying to use a global variable, since I want to catch any errors within another function.

I've tried putting 'global ftp' all over the place, and it doesn't seem to help anywhere. I have a feeling that this has something to do with the fact that FTP(ftpIP) returns a new instance of the ftp class each time it's called, but I'm not sure. Or is it not possible to declare a global object?

def ftpKeepAlive():
    global ftp
    # Keep FTP alive
    ftp.voidcmd('NOOP')         # Send a 'NOOP' command every 30 seconds

def ftpConnect():
    try:
        ftp = FTP(ftpIP)                # This times out after 20 sec
        ftp.login(XXXXX)
        ftp.cwd(ftpDirectory)

        ftp_status = 1

    except Exception, e:
        print str(e)
        ftp_status = 0
        pass



# Initialize FTP
ftpIP = '8.8.8.8'           # ftp will fail on this IP
ftp_status = 0

global ftp
ftpConnect()


while (1):
    if (second == 30):
        global ftp
        ftpKeepAlive()

Answer 1

The problem is that you define it in that many places, but you don't initialize it as needed. Try to define it only once and make sure you initialize it before trying to use it.

The code below results in the same NameError:

global ftp
ftp.voidcmd('NOOP')

But the code below results in a connection error (as expected):

from ftplib import *

global ftp
ftp = FTP('127.0.0.1')
ftp.voidcmd('NOOP')

I've made some adjustments to your code to get it closer to what I mean. Here it is:

from ftplib import *

global ftp

def ftpKeepAlive():
    # Keep FTP alive
    ftp.voidcmd('NOOP')         # Send a 'NOOP' command every 30 seconds

def ftpConnect():
    try:
        ftp = FTP(ftpIP)                # This times out after 20 sec
        ftp.login(XXXXX)
        ftp.cwd(ftpDirectory)

        ftp_status = 1

    except Exception, e:
        print str(e)
        ftp_status = 0
        pass

# Initialize FTP
ftpIP = '8.8.8.8'           # ftp will fail on this IP
ftp_status = 0

ftpConnect()

while (1):
    if (second == 30):
        ftpKeepAlive()

Answer 2

Others have provided answers to your specific question that retain use of a global variable. But you shouldn't need to use global in this manner. Instead, have ftpConnect() return the FTP client. Then you can pass that object to other functions as required. For example:

import time
from ftplib import FTP

def ftpKeepAlive(ftp):
    # Keep FTP alive
    ftp.voidcmd('NOOP')         # Send a 'NOOP' command

def ftpConnect(ftpIP, ftp_directory='.', user='', passwd=''):
    try:
        ftp = FTP(ftpIP)
        ftp.login(user, passwd)
        ftp.cwd(ftp_directory)
        return ftp
    except Exception, e:
        print str(e)

# Initialize FTP
ftpIP = '8.8.8.8'           # ftp will fail on this IP
ftp = ftpConnect(ftpIP)
if ftp:
    while (1):
        if (second == 30):
            ftpKeepAlive(ftp)
else:
    print('Failed to connect to FTP server at {}'.format(ftpIP))

Answer 3

def ftpConnect():
    global ftp, ftpIP, ftp_status       # add this...
    try:
        ftp = FTP(ftpIP)                # This times out after 20 sec
        ftp.login(XXXXX)
        ftp.cwd(ftpDirectory)

        ftp_status = 1

    except Exception, e:
        print str(e)
        ftp_status = 0
        pass