ide:pycharm；
language:python；
selenium:3.141.0
启动pycharm，并创建名为seleniumHQ的工程，创建一个py文件，输入如下代码：
if __name__ == '__main__':
from selenium.webdriver.chrome.webdriver import WebDriver
path="/Users/apple/Seleniumdriver/chromedriver"
driver = WebDriver(executable_path=path)
driver.get("https://www.baidu.com")
driver.close()
driver.quit()
进入WebDriver类源码
class WebDriver(RemoteWebDriver):
"""
Controls the ChromeDriver and allows you to drive the browser.
You will need to download the ChromeDriver executable from
http://chromedriver.storage.googleapis.com/index.html
"""
def __init__(self, executable_path="chromedriver", port=0,
options=None, service_args=None,
desired_capabilities=None, service_log_path=None,
chrome_options=None, keep_alive=True):
"""
Creates a new instance of the chrome driver.
Starts the service and then creates new instance of chrome driver.
:Args:
- executable_path - path to the executable. If the default is used it assumes the executable is in the $PATH
- port - port you would like the service to run, if left as 0, a free port will be found.
- options - this takes an instance of ChromeOptions
- service_args - List of args to pass to the driver service
- desired_capabilities - Dictionary object with non-browser specific
capabilities only, such as "proxy" or "loggingPref".
- service_log_path - Where to log information from the driver.
- chrome_options - Deprecated argument for options
- keep_alive - Whether to configure ChromeRemoteConnection to use HTTP keep-alive.
"""
if chrome_options:
warnings.warn('use options instead of chrome_options',
DeprecationWarning, stacklevel=2)
options = chrome_options
if options is None:
# desired_capabilities stays as passed in
if desired_capabilities is None:
desired_capabilities = self.create_options().to_capabilities()
else:
if desired_capabilities is None:
desired_capabilities = options.to_capabilities()
else:
desired_capabilities.update(options.to_capabilities())
self.service = Service(
executable_path,
port=port,
service_args=service_args,
log_path=service_log_path)
self.service.start()
try:
RemoteWebDriver.__init__(
self,
command_executor=ChromeRemoteConnection(
remote_server_addr=self.service.service_url,
keep_alive=keep_alive),
desired_capabilities=desired_capabilities)
except Exception:
self.quit()
raise
self._is_remote = False
其构造函数入参executable_path默认为“chromedriver”，在其init方法中，创建了一个Service类实例service，executable_path作为了Service类init方法的入参。executable_path在WebDriver源码中仅仅出现在该处，说明WebDriver在处理executable_path的过程中，仅仅只起到传递值的作用。实际处理executable_path并不在WebDriver。
进入Service类源码，
class Service(service.Service):
"""
Object that manages the starting and stopping of the ChromeDriver
"""
def __init__(self, executable_path, port=0, service_args=None,
log_path=None, env=None):
"""
Creates a new instance of the Service
:Args:
- executable_path : Path to the ChromeDriver
- port : Port the service is running on
- service_args : List of args to pass to the chromedriver service
- log_path : Path for the chromedriver service to log to"""
self.service_args = service_args or []
if log_path:
self.service_args.append('--log-path=%s' % log_path)
service.Service.__init__(self, executable_path, port=port, env=env,
start_error_message="Please see https://sites.google.com/a/chromium.org/chromedriver/home")
其init方法中将executable_path传递给了其父类的init方法，整个Service类init方法中仅将executable_path传递给了父类的init方法，未做其他处理。
进入Service的父类Service源码，
class Service(object):
def __init__(self, executable, port=0, log_file=DEVNULL, env=None, start_error_message=""):
self.path = executable
self.port = port
if self.port == 0:
self.port = utils.free_port()
if not _HAS_NATIVE_DEVNULL and log_file == DEVNULL:
log_file = open(os.devnull, 'wb')
self.start_error_message = start_error_message
self.log_file = log_file
self.env = env or os.environ
其init方法仅仅只是将executable存储下来，存在了self.path中，到此，executable_path的传递过程就结束了，但是我们仍未知道它被用在什么地方。
既然executable_path被存储在了self.path中，path是Service的一个实例属性，那么它只可能被Service类的方法所使用，回顾先前的代码，WebDriver类创建了Service类的实例service，紧接着就调用了service.start()，进入start方法，
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)
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)
在start方法中，主要都是try...except的实现。
其中将self.path放在了list类实例cmd中，并将cmd作为了参数传给subprocess.Popen函数。而subprocess.Popen函数即相当于在命令行执行了cmd命令。
所以为selenium的WebDriver init方法配置executable_path可以有两种方法：
一：将chromedriver的路径加入到环境变量Path中，而不用给WebDriver的构造方法传递任何参数，因为已经有了默认参数“chromedriver”；
二：不必配置环境变量，直接给WebDriver的init方法传递chromedriver的绝对地址，即WebDriver(executable_path=path)；
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