Python 3 UnboundLocalError：在try語句中賦值之前引用的局部變量

Question

我正在嘗試制作一個程序來處理 RSA 加密和解密，以便使用 rsa 庫發送消息。 目前我正在實施它以僅使用 1 個密鑰對，但稍后會更改。 我在檢查存儲密鑰的文件是否存在的邏輯上遇到了一些問題。 這些函數的邏輯如下所示：

import rsa

################################################
keySize = 256
################################################


def genKeys():
    pubkey, privkey = rsa.newkeys(keySize)

    with open("public.pem", "w") as pub:
        pub.write(str(pubkey))

    with open("private.pem", "w") as priv:
        priv.write(str(privkey))

    return pubkey, privkey

def readKeys():

      with open("private.pem", "r") as priv:
          keydata = priv.read()
          privkey = rsa.PrivateKey.load_pkcs1(keydata)
          print(privkey)

      with open("public.pem", "r") as pub:
          keydata = pub.read()
          pubkey = rsa.PublicKey.load_pkcs1(keydata)
          print(pubkey)
      return pubkey, privkey




def send(message, pubkey):
    message = message.encode('utf-8')
    crypto = rsa.encrypt(message, pubkey)
    return crypto

def recv(crypto, privkey):
    message = rsa.decrypt(crypto, privkey)
    message = message.decode('utf-8')
    return message

def main():
    global pubkey, privkey
    try:
        if (open("private.pem", "r") and open("public.pem", "r")) == True:

            pubkey, privkey = readKeys()

    except:
        (pubkey, privkey) = genKeys()

    cryptMessage = send('hello world', pubkey)
    print(cryptMessage)
    print(recv(cryptMessage, privkey))

if __name__ == "__main__":
    main()

main() function，特別是try: except:語句是我的問題所在。 我得到的錯誤是builtins.NameError: name 'pubkey' is not defined 。 我嘗試將變量聲明為全局變量，這是其他答案所建議的，但這對我不起作用，或者我做錯了。

謝謝您的幫助。 對不起菜鳥問題。

編輯：所以，這解決了我的第一個問題。 但是，現在當我使用try/except語句時，它會嘗試調用值為None的變量，即使我使用函數為它們分配了值。 堆棧跟蹤是

File "", line 61, in <module>
  main()
File "", line 56, in main
  cryptMessage = send('hello world', pubkey)
File "", line 37, in send
  crypto = rsa.encrypt(message, pubkey)
File "/usr/local/lib/python3.6/dist-packages/rsa/pkcs1.py", line 169, in encrypt
  keylength = common.byte_size(pub_key.n)

builtins.AttributeError: 'NoneType' object has no attribute 'n'

Answer 1

即使您將變量聲明為函數內部的全局變量，仍然需要在全局范圍內或在聲明變量時對其進行初始化。

import rsa

################################################
keySize = 256
################################################

# DECLARATION IN GLOBAL SCOPE
pubkey = None
privkey = None

def genKeys():
    pubkey, privkey = rsa.newkeys(keySize)

    with open("public.pem", "w") as pub:
        pub.write(str(pubkey))

    with open("private.pem", "w") as priv:
        priv.write(str(privkey))

    return pubkey, privkey

def readKeys():

      with open("private.pem", "r") as priv:
          keydata = priv.read()
          privkey = rsa.PrivateKey.load_pkcs1(keydata)
          print(privkey)

      with open("public.pem", "r") as pub:
          keydata = pub.read()
          pubkey = rsa.PublicKey.load_pkcs1(keydata)
          print(pubkey)
      return pubkey, privkey




def send(message, pubkey):
    message = message.encode('utf-8')
    crypto = rsa.encrypt(message, pubkey)
    return crypto

def recv(crypto, privkey):
    message = rsa.decrypt(crypto, privkey)
    message = message.decode('utf-8')
    return message

def main():
    # DECLARATION INSIDE THE FUNCTION
    global pubkey, privkey; pubkey = privkey = None
    try:
        if (open("private.pem", "r") and open("public.pem", "r")) == True:

            pubkey, privkey = readKeys()

    except:
        (pubkey, privkey) = genKeys()

    cryptMessage = send('hello world', pubkey)
    print(cryptMessage)
    print(recv(cryptMessage, privkey))

if __name__ == "__main__":
    main()

Answer 2

您應該在genKeys()函數外部聲明變量pubkey和privkey，然后錯誤應消失。 這是我的第一篇文章，希望對您有所幫助。 問候。

Answer 3

您的問題在這里：

if (open("private.pem", "r") and open("public.pem", "r")) == True:

Python邏輯運算符返回最后檢查的值，而不是True或False。 該值是來自open命令的file對象，不等於True。 您可以使用os.path.isfile檢查文件是否存在，並完全跳過try / except塊。 或者您可以嘗試在try塊中實際讀取，就像這樣

（為演示而精簡）

# dummys for test...

def readKeys():
    print('try read')
    return open('public.pem').read(), open('private.pem').read()

def genKeys():
    print('try write')
    open('public.pem','w').write('foo')
    open('private.pem','w').write('bar')
    return 'foo', 'bar'


def main():
    global pubkey, privkey
    try:
        pubkey, privkey = readKeys()
    except:
        (pubkey, privkey) = genKeys()


if __name__ == "__main__":
    main()

Answer 4

復制另一個答案的代碼並進行更改以檢查globals()而不是在每次 function 調用時覆蓋None變量。

import rsa

################################################
keySize = 256
################################################

# DECLARATION IN GLOBAL SCOPE
pubkey = None
privkey = None

def genKeys():
    pubkey, privkey = rsa.newkeys(keySize)

    with open("public.pem", "w") as pub:
        pub.write(str(pubkey))

    with open("private.pem", "w") as priv:
        priv.write(str(privkey))

    return pubkey, privkey

def readKeys():

      with open("private.pem", "r") as priv:
          keydata = priv.read()
          privkey = rsa.PrivateKey.load_pkcs1(keydata)
          print(privkey)

      with open("public.pem", "r") as pub:
          keydata = pub.read()
          pubkey = rsa.PublicKey.load_pkcs1(keydata)
          print(pubkey)
      return pubkey, privkey




def send(message, pubkey):
    message = message.encode('utf-8')
    crypto = rsa.encrypt(message, pubkey)
    return crypto

def recv(crypto, privkey):
    message = rsa.decrypt(crypto, privkey)
    message = message.decode('utf-8')
    return message

def main():
    # DECLARATION INSIDE THE FUNCTION
    global pubkey, privkey;
    if 'pubkey' not in globals() or 'privkey' not in in globals():
        pubkey = privkey = None
    try:
        if (open("private.pem", "r") and open("public.pem", "r")) == True:
            if 'pubkey' in globals() and 'privkey' in globals():
                pubkey, privkey = readKeys()
            
    except:
        if 'pubkey' in globals() and 'privkey' in globals():
            (pubkey, privkey) = genKeys()


    if 'pubkey' in globals() and 'privkey' in globals():
        cryptMessage = send('hello world', pubkey)
        print(cryptMessage)
        print(recv(cryptMessage, privkey))

if __name__ == "__main__":
    main()

這是未經測試的。 我對局部變量執行此操作，而不是在 finally 塊中關閉了本地連接 object。 為此，我什至不必在任何時候將對象設置為None ，因為我在關閉它之前檢查了連接 object 是否在globals()中。 錯誤消失了。

然而，在這段代碼中，您不僅關閉了對象，還覆蓋了它們，無論是在try塊中還是在except塊中。 因此，我只是猜測您需要在第一次加載時創建None對象。 如果這個技巧也適用於全局變量，那么這將是唯一不會在每次調用 function 時用None覆蓋全局對象的代碼，但前提是第一次接觸到變量。