最近需要使用一下selenium,刚运行就报错了。。。
前提准备：
1.安装selenium
2.下载chrome对应版本的chromedriver
代码就是一个简单的demo:

from selenium import webdriver
import time

browser = webdriver.Chrome()
browser.get('http://www.baidu.com/')
time.sleep(10)

运行报错：

网上说要把chromedriver放到环境变量，放进去还是报错！！
然后就直接看源码吧：
这个过程很繁琐，很枯燥，嫌废话连篇请直接翻到文末解决方法~~
这个过程很繁琐，很枯燥，嫌废话连篇请直接翻到文末解决方法~~
这个过程很繁琐，很枯燥，嫌废话连篇请直接翻到文末解决方法~~
1.代码报错入口:

browser = webdriver.Chrome()

2.首先看报错被挂起的地方：

File “E:\APP_Install\python_install\lib\site-packages\selenium\webdriver\common\service.py”, line 83, in start
os.path.basename(self.path), self.start_error_message)

对应代码：

    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=system() != 'Windows',
                                            stdout=self.log_file,
                                            stderr=self.log_file,
                                            stdin=PIPE,
                                            creationflags=self.creationflags)
        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

3.是start()方法的try失败了，这里可以看到是self.path的问题,再往上回溯看调用start方法的地方，self.path = executable找到传值 executable的地方：

File “E:\APP_Install\python_install\lib\site-packages\selenium\webdriver\chromium\webdriver.py”, line 90, in init
self.service.start()

相关代码如下：

class ChromiumDriver(RemoteWebDriver):
    """
    Controls the WebDriver instance of ChromiumDriver and allows you to drive the browser.
    """

    def __init__(self, browser_name, vendor_prefix,
                 port=DEFAULT_PORT, options: BaseOptions = None, service_args=None,
                 desired_capabilities=None, service_log_path=DEFAULT_SERVICE_LOG_PATH,
                 service: Service = None, keep_alive=DEFAULT_KEEP_ALIVE):
        if desired_capabilities:
            warnings.warn('desired_capabilities has been deprecated, please pass in a Service object',
                          DeprecationWarning, stacklevel=2)
        if port != DEFAULT_PORT:
            warnings.warn('port has been deprecated, please pass in a Service object',
                          DeprecationWarning, stacklevel=2)
        self.port = port
        if service_log_path != DEFAULT_SERVICE_LOG_PATH:
            warnings.warn('service_log_path has been deprecated, please pass in a Service object',
                          DeprecationWarning, stacklevel=2)
        if keep_alive != DEFAULT_KEEP_ALIVE and type(self) == __class__:
            warnings.warn('keep_alive has been deprecated, please pass in a Service object',
                          DeprecationWarning, stacklevel=2)
        else:
            keep_alive = True

        self.vendor_prefix = vendor_prefix

        _ignore_proxy = None
        if not options:
            options = self.create_options()

        if desired_capabilities:
            for key, value in desired_capabilities.items():
                options.set_capability(key, value)

        if options._ignore_local_proxy:
            _ignore_proxy = options._ignore_local_proxy

        if not service:
            raise AttributeError('service cannot be None')

        self.service = service
        self.service.start()

4.粗看似乎没什么问题，self.service.start()前面并没有进行什么特殊定义和处理，并没有进行传参"self.path",这时候就要考虑python 的继承问题了，我进入它的父类RemoteWebDriver也没有发现导致该报错的问题，这时就要考虑子类了，我们此时还忽略了一个问题：报错入口： browser = webdriver.Chrome()

webdriver.Chrome()代码如下：

E:\APP_Install\python_install\Lib\site-packages\selenium\webdriver\chrome\webdriver.py

class WebDriver(ChromiumDriver):
    def __init__(self, executable_path=DEFAULT_EXECUTABLE_PATH, port=DEFAULT_PORT,
                 options: Options = None, service_args=None,
                 desired_capabilities=None, service_log_path=DEFAULT_SERVICE_LOG_PATH,
                 chrome_options=None, service: Service = None, keep_alive=DEFAULT_KEEP_ALIVE):
        if executable_path != 'chromedriver':
            warnings.warn('executable_path has been deprecated, please pass in a Service object',
                          DeprecationWarning, stacklevel=2)
        if chrome_options:
            warnings.warn('use options instead of chrome_options',
                          DeprecationWarning, stacklevel=2)
            options = chrome_options
        if keep_alive != DEFAULT_KEEP_ALIVE:
            warnings.warn('keep_alive has been deprecated, please pass in a Service object',
                          DeprecationWarning, stacklevel=2)
        else:
            keep_alive = True
        if not service:
            service = Service(executable_path, port, service_args, service_log_path)

        super(WebDriver, self).__init__(DesiredCapabilities.CHROME['browserName'], "goog",
                                        port, options,
                                        service_args, desired_capabilities,
                                        service_log_path, service, keep_alive)

5.这不就连起来了吗，子类调用父类的__init__方法：

super(WebDriver, self).__init__ #和第3步相连

6.这个时候我们要关注Service类的传参，即super(WebDriver, self).__init__的倒数第二个参数service:

service = Service(executable_path, port, service_args, service_log_path)

对应代码：

E:\APP_Install\python_install\Lib\site-packages\selenium\webdriver\chrome\service.py

class Service(service.ChromiumService):
    def __init__(self, executable_path: str = DEFAULT_EXECUTABLE_PATH,
                 port: int = 0, service_args: List[str] = None,
                 log_path: str = None, env: dict = None):
        super(Service, self).__init__(
            executable_path,
            port,
            service_args,
            log_path,
            env,
            "Please see https://chromedriver.chromium.org/home")

这里有同学可能有疑问了？
此处的Service和第2步的Service不是一个类啊！
是的，这里还有两层嵌套关系，直接ctrl点击进去就可以看：

1.super(Service, self).__init__
2.service.Service.__init__(self, executable_path, port=port, env=env, start_error_message=start_error_message)

7.根据第6步的关系我们知道：在第2步Service出现问题的self.path就是这里面的executable_path，我们来看下这个参数的定义：

executable_path=DEFAULT_EXECUTABLE_PATH

8.刨根究底来看这个常量的定义：

DEFAULT_EXECUTABLE_PATH = "chromedriver"

9.这不就出来了，定义的executable_path 解释器没有找到，就直接使用chromedriver了，所以导致报错，我们确认一下这个参数的定义：

- executable_path - Deprecated: path to the executable. If the default is used it assumes the executable is in the $PATH

10.至此，有两个解决办法：
1.直接修改DEFAULT_EXECUTABLE_PATH 为你机器的chromedriver的路径
哈哈，但是这个方法只适用于你的机器了，因此我们考虑脚本传参executable_path：
那不就是第一个参数吗？直接传进去，大功告成：

from selenium import webdriver
import time

browser = webdriver.Chrome("F:\google_download\chromedriver_99.0/chromedriver.exe")
browser.get('http://www.baidu.com/')
time.sleep(10)