为什么 strip() 修复了这个 pexpect 脚本？
我有一个对象。
该对象有一个 connect() 方法，该方法会生成一个 pexpect 进程。
生成的进程是一个自定义串行接口。启动时，该工具会打印要连接的串行设备的菜单，如下所示：
libftdi device (0): A6005jpt libftdi 设备 (1)：acFX9DQf 串行设备（a）：/dev/cu.Bluetooth-PDA-Sync 通过字母选择设备（^D 表示中止）：
我的 connect() 根据给定的设备名称（例如“acFX9DQf”）确定要传递的数字：（self.connection 是pexpect 生成）
USBSERIAL_DEVICE_NAME = "acFX9DQf"
try:
while self.connection.expect(['libftdi device \(([0-9])\): (.*)','Serial device']) == 0:
if self.connection.match.group(2).strip() == USBSERIAL_DEVICE_NAME:
# do stuff
except:
# do stuff
现在，我的问题是我在主逻辑中多次 connect()/kill() 进程，有时，其中一次，连接()决定意外地抛出 pexpect.TIMEOUT 异常。
例如，当我将以下调试语句添加到我的逻辑中时，如下所示：
USBSERIAL_DEVICE_NAME = "acFX9DQf"
try:
while self.connection.expect(['libftdi device \(([0-9])\): (.*)','Serial device'], timeout=10) == 0:
print "MATCHED A DEVICE LINE!"
if self.connection.match.group(2).strip() == USBSERIAL_DEVICE_NAME:
print "MATCHED THE DESIRED USBSERIAL..."
...对于 connect() 的多次调用，我得到此输出：
libftdi device (0): A6005jpt 匹配设备系列！ libftdi 设备 (1)：acFX9DQf 匹配设备系列！ 匹配所需的 USB 串口... 串行设备（a）：/dev/cu.Bluetooth-PDA-Sync 按字母选择设备（^D 表示中止）：1
...然后，我的一个 connect() 调用将意外地执行...
libftdi device ( 0): A6005jpt 匹配设备系列！ libftdi 设备 (1)：acFX9DQf 串行设备（a）：/dev/cu.Bluetooth-PDA-Sync 按字母选择设备（^D 中止）：匹配设备线！ <>
但是，如果我将代码修改为：
try:
while self.connection.expect(['libftdi device \(([0-9])\): (.*)','Serial device'], timeout=10) == 0:
devicename = self.connection.match.group(2).strip()
if devicename == USBSERIAL_DEVICE_NAME:
# do stuff
我的问题就会消失！我可以重复运行它，不会出现任何问题 - 没有例外，没有任何问题。
那么这里到底发生了什么？我什至不知道从哪里开始解决这个问题。
I have an object.
This object has a connect() method which spawns a pexpect process.
The process that's spawned is a custom serial interface. On launch, this tool prints a menu of serial devices to connect to, like so:
libftdi device (0): A6005jpt libftdi device (1): acFX9DQf Serial device (a) : /dev/cu.Bluetooth-PDA-Sync Select a device by its letter (^D to abort):
My connect() determines which number to pass based on a given devicename (e.g. 'acFX9DQf'): (self.connection is the pexpect spawn)
USBSERIAL_DEVICE_NAME = "acFX9DQf"
try:
while self.connection.expect(['libftdi device \(([0-9])\): (.*)','Serial device']) == 0:
if self.connection.match.group(2).strip() == USBSERIAL_DEVICE_NAME:
# do stuff
except:
# do stuff
Now, my problem is that I connect()/kill() the process multiple times in my main logic and sometimes, one of those times, connect() decides to throw a pexpect.TIMEOUT exception, unexpectedly.
For example, when I add the following debug statements to my logic, like so:
USBSERIAL_DEVICE_NAME = "acFX9DQf"
try:
while self.connection.expect(['libftdi device \(([0-9])\): (.*)','Serial device'], timeout=10) == 0:
print "MATCHED A DEVICE LINE!"
if self.connection.match.group(2).strip() == USBSERIAL_DEVICE_NAME:
print "MATCHED THE DESIRED USBSERIAL..."
...I get this output for many calls of connect():
libftdi device (0): A6005jpt MATCHED A DEVICE LINE! libftdi device (1): acFX9DQf MATCHED A DEVICE LINE! MATCHED THE DESIRED USBSERIAL... Serial device (a) : /dev/cu.Bluetooth-PDA-Sync Select a device by its letter (^D to abort): 1
...then, one of my connect() calls will unexpectedly do....
libftdi device (0): A6005jpt MATCHED A DEVICE LINE! libftdi device (1): acFX9DQf Serial device (a) : /dev/cu.Bluetooth-PDA-Sync Select a device by its letter (^D to abort): MATCHED A DEVICE LINE! <<EXCEPTION>>
But, if I revise my code to this:
try:
while self.connection.expect(['libftdi device \(([0-9])\): (.*)','Serial device'], timeout=10) == 0:
devicename = self.connection.match.group(2).strip()
if devicename == USBSERIAL_DEVICE_NAME:
# do stuff
My problems go away! I can run it repeatedly and no problems will occur - no exceptions, no nothin'.
So wot in the heck is going on here? I'm not even sure where to begin with this problem.
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评论（1）
我猜您遇到了
TIMEOUT异常。基于“匹配设备线！”的位置消息在输出中，我的假设是spawn实例在测试匹配时有多行。当 pexpect 编译正则表达式时，它 设置re.DOTALL，因此.*包含换行符和附加行。这会导致针对USBSERIAL_DEVICE_NAME的测试失败，并且循环将继续进行下一次迭代。下一次对expect的调用会阻塞，因为没有额外的输入并且您会遇到超时。要解决此问题，您可以传入自己编译的正则表达式（它将缺少
re.DOTALL标志）或更改.*，使其明确与换行符不匹配（例如\S*）。至于为什么将匹配的组存储在变量中似乎可以解决问题，我只能猜测这会引入微妙的时间变化，从而阻止对
expect的调用同时接收多行输入。I'm guessing you're getting a
TIMEOUTexception. Based on where the "MATCHED A DEVICE LINE!" message is in the output, my hypothesis is that thespawninstance has multiple lines when it tests for a match. When pexpect compiles the regexes, it setsre.DOTALL, so the.*includes the newline and the additional lines. This causes the test againstUSBSERIAL_DEVICE_NAMEto fail and the loop continues its next iteration. The next call toexpectblocks because there is no additional input and you get a timeout.To fix this, you can pass in your own compiled regexes (which will lack the
re.DOTALLflag) or change the.*so it explicitly doesn't match the newline (e.g.\S*).As for why storing the matched group in a variable seems to fix things, I can only guess this introduces a subtle timing change that prevents the call to
expectfrom receiving multiple lines of input at once.