python - 数组初始化中 Python 中的奇怪行为

Question

在下面，您将看到我编写的用于将 APDU 命令发送到智能卡的 Python 程序片段。我在这个程序中使用了 PySCard 库。

第一个程序:

for LOAD_KEY in validLoadCommands:
    data,sw1,sw2 =connection.transmit(LOAD_KEY)
    temp = LOAD_KEY
    x= temp[3]
    for j in range(0,len(LOAD_KEY)):
        LOAD_KEY[j]=hex(LOAD_KEY[j])
    print '   >>>',' Load Command :',
    for j in range(0,len(LOAD_KEY)):
        LOAD_KEY[j]=str(LOAD_KEY[j])
        if len(LOAD_KEY[j])==3:
            LOAD_KEY[j]=LOAD_KEY[j][0:2]+'0'+LOAD_KEY[j][2]
        print LOAD_KEY[j],
    print
    for j in range(0,len(data)):
        data[j]=hex(data[j])
    print '   <<<',' Data :',
    for j in range(0,len(data)):
        data[j]=str(data[j])
        if len(data[j])==3:
            data[j]=data[j][0:2]+'0'+data[j][2]
        print data[j],
    print '--',hex(sw1),hex(sw2)

    if (temp[2] == 0x00 or temp[2] == 0x20):
        keyType = 0x60
    else:
        keyType = 0x61

    AUTH = [0xFF, 0x86, 0x00, 0x00, 0x05, 0x01, 0x00, blockNum, keyType,temp[3]]
    print 'AUTH Command: ', AUTH
    data,sw1,sw2 =connection.transmit(AUTH)
    print data, sw1, sw2

及其输出:

Auth Command: [255, 134, 0, 0, 5, 1, 0, 4, 97, '0x0e']

Traceback (most recent call last):
  File "C:\Users\Erb4h1m\Desktop\Faraadis Alborz Card Reader\CRT-603-CZ1_Read1Block.py", line 199, in <module>
    data,sw1,sw2 =connection.transmit(AUTH)
  File "D:\Software\Python27\lib\site-packages\smartcard\CardConnectionDecorator.py", line 82, in transmit
    return self.component.transmit(bytes, protocol)
  File "D:\Software\Python27\lib\site-packages\smartcard\CardConnection.py", line 140, in transmit
    data, sw1, sw2 = self.doTransmit(bytes, protocol)
  File "D:\Software\Python27\lib\site-packages\smartcard\pcsc\PCSCCardConnection.py", line 173, in doTransmit
    hresult, response = SCardTransmit(self.hcard, pcscprotocolheader, bytes)
  File "D:\Software\Python27\lib\site-packages\smartcard\scard\scard.py", line 1329, in SCardTransmit
    return _scard.SCardTransmit(*args)
TypeError: Expected a list of bytes.

当我将 temp[3] 替换为 x 时:

for LOAD_KEY in validLoadCommands:
    data,sw1,sw2 =connection.transmit(LOAD_KEY)
    temp = LOAD_KEY
    x= temp[3]
    for j in range(0,len(LOAD_KEY)):
        LOAD_KEY[j]=hex(LOAD_KEY[j])
    print '   >>>',' Load Command :',
    for j in range(0,len(LOAD_KEY)):
        LOAD_KEY[j]=str(LOAD_KEY[j])
        if len(LOAD_KEY[j])==3:
            LOAD_KEY[j]=LOAD_KEY[j][0:2]+'0'+LOAD_KEY[j][2]
        print LOAD_KEY[j],
    print
    for j in range(0,len(data)):
        data[j]=hex(data[j])
    print '   <<<',' Data :',
    for j in range(0,len(data)):
        data[j]=str(data[j])
        if len(data[j])==3:
            data[j]=data[j][0:2]+'0'+data[j][2]
        print data[j],
    print '--',hex(sw1),hex(sw2)

    if (temp[2] == 0x00 or temp[2] == 0x20):
        keyType = 0x60
    else:
        keyType = 0x61

    AUTH = [0xFF, 0x86, 0x00, 0x00, 0x05, 0x01, 0x00, blockNum, keyType, x]
    print 'AUTH Command: ', AUTH
    data,sw1,sw2 =connection.transmit(AUTH)
    print data, sw1, sw2

那么输出是:

AUTH: [255, 134, 0, 0, 5, 1, 0, 4, 97, 14]
[] 144 0

正如您在上面看到的，在第二种情况下我没有收到任何错误，而第一个程序和第二个程序之间没有区别!我只换了

    AUTH = [0xFF, 0x86, 0x00, 0x00, 0x05, 0x01, 0x00, blockNum, keyType,temp[3]]

与:

    AUTH = [0xFF, 0x86, 0x00, 0x00, 0x05, 0x01, 0x00, blockNum, keyType,x]

和 x 在程序顶部用 temp[3] 初始化。 x 和 temp[3] 都没有在初始化行和错误行之间发生变化。

这是怎么回事？

Answer 1

您的 temp 变量引用 LOAD_KEY(第 3 行:temp = LOAD_KEY)

当 x= temp[3] 被调用时，它是 connection.transmit 之后索引 3 处的 LOAD_KEY 的值设置。

当您为您的 AUTH 发送 temp[3] 时，LOAD_KEY 已更改，temp[3]。所以它不再是与 x 相同的值。

connection.transmit => LOAD_KEY is set => temp => [3] => x
*** LOAD_KEY changes ***
x => old value of temp[3] aka LOAD_KEY[3]
temp[3] => whatever your code have put in it

编辑:简短示例

>>> LOAD_KEY = ['one', 'two', 'three', 'four']
>>> temp = LOAD_KEY
>>> x = temp[3]
>>> LOAD_KEY[3] = 'new value'
>>>
>>> LOAD_KEY[3]
'new value'
>>> temp[3]
'new value'
>>> x
'four'