NameError 说变量未定义，但仅在某些地方

Question

我正在尝试实现每 30 秒发送一些数据以保持 telnet 连接打开的保持活动状态。

我的代码每秒调用 reinitScore。此函数有时会调用 calculateWinner，它通过 stelnet.send(data).

通过 telnet 发送数据

问题是，当我在任何函数中调用 stelnet.send(data) 时，它会引发 NameError: global name 'stelnet' is not defined.

我的问题是：为什么 stelnet.send(data) 在一个地方工作，而不在另一个地方工作？

这是我的代码中涉及 telnet 传输和函数调用的部分：

import socket, select, string, sys
import string
import threading

leftKeyCounter = 0
rightKeyCounter = 0
frontKeyCounter = 0
backKeyCounter = 0

# function called by reinitScore
def calculateWinner(d):
    scores = {}
    high_score = 0
    for key, value in d.items():
        try:
            scores[value].append(key)
        except KeyError:
            scores[value] = [key]
        if value > high_score:
            high_score = value
    results = scores[high_score]
    if len(results) == 1:
        print results[0]
        stelnet.send(results[0])
        return results[0]
    else:
        print 'TIE'
        return 'TIE', results

#called once and repeat itselfs every second
def reinitScore():
    threading.Timer(1, reinitScore).start()
    #globaling for changing the content
    global leftKeyCounter
    global rightKeyCounter
    global frontKeyCounter
    global backKeyCounter
    values = {'left' : leftKeyCounter, 'right' : rightKeyCounter, 'front' : frontKeyCounter, 'back' : backKeyCounter}
    if (leftKeyCounter != 0 or rightKeyCounter != 0 or frontKeyCounter != 0 or backKeyCounter != 0):
        calculateWinner(values)
        leftKeyCounter = 0
        rightKeyCounter = 0
        frontKeyCounter = 0
        backKeyCounter = 0
        print "back to 0"

reinitScore()
if __name__ == "__main__":

    if(len(sys.argv) < 3) :


    print 'Usage : python telnet.py hostname port'
    sys.exit()

    host = sys.argv[1]
    port = int(sys.argv[2]) 
    stelnet = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    stelnet.settimeout(2)

    # connect to remote host
    try :
        stelnet.connect((host, port))
    except :
        print 'Unable to connect'
        sys.exit()

    print 'Connected to remote host'

    while True:
       // ... Some code that has nothing to do with telnet 

    while 1:
       socket_list = [sys.stdin, stelnet]

        read_sockets, write_sockets, error_sockets = select.select(socket_list , [], [])

        for sock in read_sockets:
            if sock == stelnet:
                data = sock.recv(4096)
                if not data :
                    print 'Connection closed'
                    sys.exit()
                else :
                    sys.stdout.write(data)

            else :
                msg = sys.stdin.readline()
                stelnet.send(msg)

我试图在很多地方将 stelnet 声明为 global 变量，但它没有改变任何东西 --- 我总是得到 "not defined" NameError .

Answer 1

您的代码无法正常工作，因为您没有将 stelnet 传递给您的函数。

Answer 2

响应您更新的代码...错误消息仍然正确，因为尽管您在模块级别定义了stelnet，但您已经定义了太晚了。它的定义发生在之后它在calculateWinner函数中的使用。

将您的代码简化为一个可笑的最小示例，您正在做这样的事情：

def calculateWinner():
    # A leap of faith...  There is no `stelnet` defined
    # in this function.
    stelnet.send(results[0])

def reinitScore():
    # Indirectly depends on `stelnet` too.
    calculateWinner()

# But we haven't defined `stelnet` yet...
reinitScore() # Kaboom!

# These lines will never run, because the NameError has
# already happened.
if __name__ == '__main__':
    stelnet = ...  # Too late.

calculateWinner 依赖于函数编译时 不存在 的名称。它是否有效或崩溃取决于其他代码是否定义了 stelnet 1) calculateWinner 可以获取它的位置，以及 2) 在执行 calculateWinner 之前。

建议

依赖于全局可变状态的函数很难理解，更不用说正确编码了。很难分辨什么取决于哪些变量，或者什么在修改它们，或者什么时候。此外，想出一个 MCVE 比它应该的更麻烦，因为看起来独立的函数可能不是。

将尽可能多的模块级代码填充到 main 函数中，并从 if __name__ == '__main__': 函数体中调用它（仅此而已）（因为甚至那个实际上是在模块级别）。

考虑这样的事情：

def reinit_score(output_socket, shared_scores):
    # Ensuring safe concurrent access to the `shared_scores`
    # dictionary is left as an exercise for the reader.
    winner = ...  # Determined from `shared_scores`.
    output_socket.send(winner)
    for key in shared_scores:
        shared_scores[key] = 0
    threading.Timer(
      interval=1,
      function=reinit_score,
      args=[output_socket, shared_scores],
      ).start()

def main():
    output_socket = ...  # This was `stelnet`.
    shared_scores = {...}  # A dictionary with 4 keys: L/R/U/D.
    reinit_score(output_socket, shared_scores)
    while True:
        play_game(shared_scores)
        # `play_game` mutates the `shared_scores` dictionary...

if __name__ == '__main__':
    main()

这些函数仍然通过它们传递的共享字典连接，但只有明确传递给该字典的函数才能更改其内容。

NameError 说变量未定义，但仅在某些地方

NameError says variable is not defined, but only in some places

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