python - 子类化对象导致 NoneType

Question

我尝试对 Chrome WebDriver 进行子类化以包含一些初始化和清理代码，但随后 Python 提示创建的对象设置为 None:

import glob
import selenium
import subprocess
from selenium.webdriver.common.by import By


class WebDriver(selenium.webdriver.Chrome):
    def __init__(self, url, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.url = url

    def __enter__(self):
        self.get(self.url)
        self.implicitly_wait(15)

    def __exit__(self, type, value, traceback):
        self.quit()
        for path in glob.glob('/tmp/.org.chromium.Chromium.*'):
            subprocess.run(['rm', '-rf', path], check=True)


with WebDriver('https://google.com') as driver:
    driver.find_element(By.ID, 'lst-ib').send_keys('Search')

使用 Python 3 运行代码:

$ python3 test.py
Traceback (most recent call last):
  File "test.py", line 43, in <module>
    driver.find_element(By.ID, 'lst-ib').send_keys('Search')
AttributeError: 'NoneType' object has no attribute 'find_element'

Answer 1

你的__enter__()魔术方法应该返回self，以便driver变量指向WebDriver<的实例类:

def __enter__(self):
    self.get(self.url)
    self.implicitly_wait(15)
    return self

要获取有关其工作原理和原理的更多信息，请参阅:

• Understanding Python's "with" statement
• Explaining Python's '__enter__' and '__exit__'