子类对象导致 NoneType

Question

我正在尝试子类化 Chrome WebDriver 以包含一些初始化和清理代码，但是 Python 抱怨创建的对象设置为 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')

运行代码与 Python 3:

$ 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 return self 使 driver 变量指向 WebDriver class 的实例:

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

要了解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__'

子类对象导致 NoneType

Subclassed object results in NoneType

python

selenium

subclass

python-3.x