python - 在不关闭 Python 中的 Selenium Webdriver session 的情况下捕获 `KeyboardInterrupt`

Question

一个 Python 程序通过 Selenium WebDriver 驱动 Firefox。代码嵌入在 try/except block 中，如下所示:

session = selenium.webdriver.Firefox(firefox_profile)
try:
    # do stuff
except (Exception, KeyboardInterrupt) as exception:
    logging.info("Caught exception.")
    traceback.print_exc(file=sys.stdout)

如果程序因错误而中止，WebDriver session 不会关闭，因此 Firefox 窗口保持打开状态。但是如果程序因 KeyboardInterrupt 异常而中止，Firefox 窗口就会关闭(我想是因为 WebDriver session 也被释放了)，我想避免这种情况。

我知道这两个异常都通过同一个处理程序，因为我在这两种情况下都看到了 "Caught exception" 消息。

如何避免使用 KeyboardInterrupt 关闭 Firefox 窗口？

Answer 1

我有一个解决方案，但它很丑。

当按下 Ctrl+C 时，python 会收到一个中断信号 (SIGINT)，该信号会在整个进程树中传播。Python 还会生成一个 KeyboardInterrupt，因此您可以尝试处理与您的进程的逻辑绑定(bind)的东西，但与子进程耦合的逻辑不会受到影响。

要影响将哪些信号传递给您的子进程，您必须在通过 subprocess.Popen 生成进程之前指定应如何处理信号。

有多种选择，这个取自another answer :

import subprocess
import signal

def preexec_function():
    # Ignore the SIGINT signal by setting the handler to the standard
    # signal handler SIG_IGN.
    signal.signal(signal.SIGINT, signal.SIG_IGN)

my_process = subprocess.Popen(
    ["my_executable"],
    preexec_fn = preexec_function
)

问题是，调用Popen的不是你，即delegated to selenium .有various discussions就这样。根据我收集到的其他解决方案，如果在调用 Popen 之前未立即执行屏蔽，则其他尝试影响信号屏蔽的解决方案很容易失败。

另外请记住，有一个 big fat warning regarding the use of preexec_fn in the python documentation ，因此请自行决定使用它。

“幸运”python 允许在运行时覆盖函数，所以我们可以这样做:

>>> import monkey
>>> import selenium.webdriver
>>> selenium.webdriver.common.service.Service.start = monkey.start
>>> ffx = selenium.webdriver.Firefox()
>>> # pressed Ctrl+C, window stays open.
KeyboardInterrupt
>>> ffx.service.assert_process_still_running()
>>> ffx.quit()
>>> ffx.service.assert_process_still_running()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.6/site-packages/selenium/webdriver/common/service.py", line 107, in assert_process_still_running
    return_code = self.process.poll()
AttributeError: 'NoneType' object has no attribute 'poll'

与 monkey.py 如下:

import errno
import os
import platform
import subprocess
from subprocess import PIPE
import signal
import time
from selenium.common.exceptions import WebDriverException
from selenium.webdriver.common import utils

def preexec_function():
    signal.signal(signal.SIGINT, signal.SIG_IGN)

def start(self):
  """
        Starts the Service.
        :Exceptions:
         - WebDriverException : Raised either when it can't start the service
           or when it can't connect to the service
        """
  try:
    cmd = [self.path]
    cmd.extend(self.command_line_args())
    self.process = subprocess.Popen(cmd, env=self.env,
                                    close_fds=platform.system() != 'Windows',
                                    stdout=self.log_file,
                                    stderr=self.log_file,
                                    stdin=PIPE,
                                    preexec_fn=preexec_function)
#                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  except TypeError:
    raise
  except OSError as err:
    if err.errno == errno.ENOENT:
      raise WebDriverException(
        "'%s' executable needs to be in PATH. %s" % (
          os.path.basename(self.path), self.start_error_message)
      )
    elif err.errno == errno.EACCES:
      raise WebDriverException(
        "'%s' executable may have wrong permissions. %s" % (
          os.path.basename(self.path), self.start_error_message)
      )
    else:
      raise
  except Exception as e:
    raise WebDriverException(
      "The executable %s needs to be available in the path. %s\n%s" %
      (os.path.basename(self.path), self.start_error_message, str(e)))
  count = 0
  while True:
    self.assert_process_still_running()
    if self.is_connectable():
      break
    count += 1
    time.sleep(1)
    if count == 30:
      raise WebDriverException("Can not connect to the Service %s" % self.path)

code for start is from selenium ，添加的行突出显示。这是一个粗略的黑客，它可能会咬你。祝你好运:D