本文感谢以下文档或说明提供的参考。
Selenium-Python中文文档
>Selenium Documentation
>Webdriver 参考
如有错误欢迎在评论区指出，作者将即时更改。
环境说明
- 操作系统：Windows7 SP1 64
- python 版本：3.7.7
- 浏览器：谷歌浏览器
- 浏览器版本： 80.0.3987 (64 位)
- 谷歌浏览器驱动：驱动版本需要对应浏览器版本，不同的浏览器使用对应不同版本的驱动，点击下载
- 如果是使用火狐浏览器，查看火狐浏览器版本，点击 GitHub火狐驱动下载地址 下载（英文不好的同学右键一键翻译即可，每个版本都有对应浏览器版本的使用说明，看清楚下载即可）
简介
Selenium 是一个涵盖了一系列工具和库的总体项目，这些工具和库支持 Web 浏览器的自动化。并且在执行自动化时，所进行的操作会像真实用户操作一样。
Selenium 有 3 个版本，分别是 Selenium 1.0、Selenium2.0、Selenium3.0；
Selenium 1.0 主要是调用 JS 注入到浏览器；最开始 Selenium 的作者 Jason Huggins 开发了 JavaScriptTestRunner 作为测试工具，当时向多位同事进行了展示（这个作者也是个很有趣的灵魂）。从这个测试工具的名字上可以看出，是基于 JavaScript 进行的测试。这个工具也就是 Selenium 的“前身”。
Selenium 2.0 基于 WebDriver 提供的 API，进行浏览器的元素操作。WebDriver 是一个测试框架也可以说是一个集成的 API 接口库。
Selenium 3.0 基于 Selenium 2.0 进行扩展，基本差别不大；本文将以 Selenium 3.0 版本进行技术说明。
在官方介绍中介绍了有关支持浏览器的说明：“通过 WebDriver，Selenium 支持市场上所有主流浏览器，例如 Chrom（ium），Firefox，Internet Explorer，Opera 和 Safari。”
简单开始
安装好环境后，简单的使用 selenium 让浏览器打开 CSDN 官网。
在环境配置时需要注意：必须把驱动给配置到系统环境，或者丢到你 python 的根目录下。
首先引入 webdriver ：
from selenium.webdriver import Chrome
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当然也可以：
from selenium import webdriver
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引入方式因人而异，之后使用不同的方法新建不同的实例。
from selenium.webdriver import Chromedriver = Chrome()
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或者
from selenium import webdriverdriver = webdriver.Chrome()
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一般性的 python 语法将不会在下文赘述。
之前所提到，需要把驱动配置到系统环境之中，但不外乎由于其它原因导致的不能驱动路径不能加入到系统环境中，在这里提供一个解决方法：
from selenium import webdriverdriver = webdriver.Chrome(executable_path=r'F:\python\dr\chromedriver_win32\chromedriver.exe')
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这里使用 executable_path 指定驱动地址，这个地址是我驱动所存放的位置。当然这个位置可以根据自己需求制定，并且以更加灵活；本文为了更好说明，所以使用了绝对路径传入。
火狐浏览器：
from selenium import webdriver
driver = webdriver.Firefox()driver.get("http://www.csdn.net")
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谷歌浏览器：
from selenium import webdriver
driver = webdriver.Chrome()driver.get("http://www.csdn.net")
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火狐浏览器与谷歌浏览器只有实例化方法不同，其它的操作方法均一致。
在代码最开头引入 webdriver ，在代码中实例化浏览器对象后，使用 get 方法请求网址，打开所需要的网址。
实现剖析
查看 webdriver.py 实现（from selenium import webdriver）：
import warnings
from selenium.webdriver.remote.webdriver import WebDriver as RemoteWebDriverfrom .remote_connection import ChromeRemoteConnectionfrom .service import Servicefrom .options import Options
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
def launch_app(self, id): """Launches Chrome app specified by id.""" return self.execute("launchApp", {'id': id})
def get_network_conditions(self): return self.execute("getNetworkConditions")['value']
def set_network_conditions(self, **network_conditions): self.execute("setNetworkConditions", { 'network_conditions': network_conditions })
def execute_cdp_cmd(self, cmd, cmd_args): return self.execute("executeCdpCommand", {'cmd': cmd, 'params': cmd_args})['value']
def quit(self): try: RemoteWebDriver.quit(self) except Exception: # We don't care about the message because something probably has gone wrong pass finally: self.service.stop()
def create_options(self): return Options()
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从注释中表明这是 “创建 chrome 驱动程序的新实例，并且创建 chrome 驱动程序的实例”。
在此只列出本篇文章使用到的参数：
- executable_path：可执行文件的路径。如果使用默认值，则假定可执行文件位于 PATH 中；其中的 PATH 为系统环境根目录
在 selenium 实现自动化过程中，必要的一步是启动服务，查看 init 初始化方法中，发现了以下代码：
self.service = Service( executable_path, port=port, service_args=service_args, log_path=service_log_path)self.service.start()
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以上代码实例化了 Service 类，并且传入相关参数，之后启动服务；在这里最主要的参数为 executable_path，也就是启动驱动。查看 Service 类（selenium.service）：
from selenium.webdriver.common import service
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")
def command_line_args(self): return ["--port=%d" % self.port] + self.service_args
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查看基类 start 方法实现（由于基类过长不全部展出，基类在 selenium.webdriver.common import service 中）：
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)
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其中发现：
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)
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启动子进程开启驱动。在出现异常时接收抛出异常并且报错。开启驱动打开浏览器。
在异常抛出检测到此已知道了 selenium 如何启动服务。接下来查看 get 请求网址的实现流程。
查看 webdriver 基类（selenium.webdriver.remote.webdriver），找到 get 方法：
def get(self, url): """ Loads a web page in the current browser session. """ self.execute(Command.GET, {'url': url})
def execute(self, driver_command, params=None): """ Sends a command to be executed by a command.CommandExecutor.
:Args: - driver_command: The name of the command to execute as a string. - params: A dictionary of named parameters to send with the command.
:Returns: The command's JSON response loaded into a dictionary object. """ if self.session_id is not None: if not params: params = {'sessionId': self.session_id} elif 'sessionId' not in params: params['sessionId'] = self.session_id
params = self._wrap_value(params) response = self.command_executor.execute(driver_command, params) if response: self.error_handler.check_response(response) response['value'] = self._unwrap_value( response.get('value', None)) return response # If the server doesn't send a response, assume the command was # a success return {'success': 0, 'value': None, 'sessionId': self.session_id}
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通过 get 方法得知，调用了 execute 方法，传入了 Command.GET 与 url。
查看 Command.GET 的类 Command（selenium.webdriver.remote.command）得知，Command 为标准 WebDriver 命令的常量；找到 GET 常量：
从文件上，应该是执行命令方式的类文件。
首先整理一下流程：
- 启动服务→调用 get 方法
其中 get 方法具体流程：
- get 方法调用 execute 方法，传入参数为 Command.GET 与 url，查看 Command 的值是标准常量。 在 execute 方法中，
其中 execute 的实现为：
def execute(self, driver_command, params=None): """ Sends a command to be executed by a command.CommandExecutor.
:Args: - driver_command: The name of the command to execute as a string. - params: A dictionary of named parameters to send with the command.
:Returns: The command's JSON response loaded into a dictionary object. """ if self.session_id is not None: if not params: params = {'sessionId': self.session_id} elif 'sessionId' not in params: params['sessionId'] = self.session_id
params = self._wrap_value(params) response = self.command_executor.execute(driver_command, params) if response: self.error_handler.check_response(response) response['value'] = self._unwrap_value( response.get('value', None)) return response # If the server doesn't send a response, assume the command was # a success return {'success': 0, 'value': None, 'sessionId': self.session_id}
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其中核心代码为：
params = self._wrap_value(params)response = self.command_executor.execute(driver_command, params)if response: self.error_handler.check_response(response) response['value'] = self._unwrap_value( response.get('value', None)) return response
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主要查看：
self.command_executor.execute(driver_command, params)
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其中 commandexecutor 为初始化后实例，查看派生类 webdriver（selenium import webdriver） commandexecutor 的实例化为：
RemoteWebDriver.__init__( self, command_executor=ChromeRemoteConnection( remote_server_addr=self.service.service_url, keep_alive=keep_alive), desired_capabilities=desired_capabilities)
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查看 ChromeRemoteConnection 类（selenium import remote_connection）：
from selenium.webdriver.remote.remote_connection import RemoteConnection
class ChromeRemoteConnection(RemoteConnection):
def __init__(self, remote_server_addr, keep_alive=True): RemoteConnection.__init__(self, remote_server_addr, keep_alive) self._commands["launchApp"] = ('POST', '/session/$sessionId/chromium/launch_app') self._commands["setNetworkConditions"] = ('POST', '/session/$sessionId/chromium/network_conditions') self._commands["getNetworkConditions"] = ('GET', '/session/$sessionId/chromium/network_conditions') self._commands['executeCdpCommand'] = ('POST', '/session/$sessionId/goog/cdp/execute')
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得知调用的是基类初始化方法，查看得知 execute 方法实现为：
def execute(self, command, params): """ Send a command to the remote server.
Any path subtitutions required for the URL mapped to the command should be included in the command parameters.
:Args: - command - A string specifying the command to execute. - params - A dictionary of named parameters to send with the command as its JSON payload. """ command_info = self._commands[command] assert command_info is not None, 'Unrecognised command %s' % command path = string.Template(command_info[1]).substitute(params) if hasattr(self, 'w3c') and self.w3c and isinstance(params, dict) and 'sessionId' in params: del params['sessionId'] data = utils.dump_json(params) url = '%s%s' % (self._url, path) return self._request(command_info[0], url, body=data)
def _request(self, method, url, body=None): """ Send an HTTP request to the remote server.
:Args: - method - A string for the HTTP method to send the request with. - url - A string for the URL to send the request to. - body - A string for request body. Ignored unless method is POST or PUT.
:Returns: A dictionary with the server's parsed JSON response. """ LOGGER.debug('%s %s %s' % (method, url, body))
parsed_url = parse.urlparse(url) headers = self.get_remote_connection_headers(parsed_url, self.keep_alive) resp = None if body and method != 'POST' and method != 'PUT': body = None
if self.keep_alive: resp = self._conn.request(method, url, body=body, headers=headers)
statuscode = resp.status else: http = urllib3.PoolManager(timeout=self._timeout) resp = http.request(method, url, body=body, headers=headers)
statuscode = resp.status if not hasattr(resp, 'getheader'): if hasattr(resp.headers, 'getheader'): resp.getheader = lambda x: resp.headers.getheader(x) elif hasattr(resp.headers, 'get'): resp.getheader = lambda x: resp.headers.get(x)
data = resp.data.decode('UTF-8') try: if 300 <= statuscode < 304: return self._request('GET', resp.getheader('location')) if 399 < statuscode <= 500: return {'status': statuscode, 'value': data} content_type = [] if resp.getheader('Content-Type') is not None: content_type = resp.getheader('Content-Type').split(';') if not any([x.startswith('image/png') for x in content_type]):
try: data = utils.load_json(data.strip()) except ValueError: if 199 < statuscode < 300: status = ErrorCode.SUCCESS else: status = ErrorCode.UNKNOWN_ERROR return {'status': status, 'value': data.strip()}
# Some of the drivers incorrectly return a response # with no 'value' field when they should return null. if 'value' not in data: data['value'] = None return data else: data = {'status': 0, 'value': data} return data finally: LOGGER.debug("Finished Request") resp.close()
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从以上实现得知，execute 为向远程服务器发送请求；execute 中调用的_request 方法为发送 http 请求并且返回相关结果，请求结果通过浏览器进行响应。
官方说明中说明了请求原理：
At its minimum, WebDriver talks to a browser through a driver.
Communication is two way: WebDriver passes commands to the browser through the driver, and receives information back via the same route.
The driver is specific to the browser, such as ChromeDriver for Google’s Chrome/Chromium, GeckoDriver for Mozilla’s Firefox, etc. Thedriver runs on the same system as the browser. This may, or may not be, the same system where the tests themselves are executing.
This simple example above is direct communication. Communication to the browser may also be remote communication through Selenium Server or RemoteWebDriver. RemoteWebDriver runs on the same system as the driver and the browser.
言而总之我们通过 webdriver 与浏览器进行对话，从而浏览器进行响应。
通过以上实例得知，使用 execute 向远程服务器发送请求会通过 webdriver 与浏览器交互，且发送已定义的命令常量可获得一些相关信息。
由于在代码中我们实例的是 webdriver 实例，去 webdriver 基类（selenium.webdriver.remote.webdriver）中查询相关信息，是否有相关函数可以获取信息。发现以下函数：
def title(self): """Returns the title of the current page.
:Usage: title = driver.title """ resp = self.execute(Command.GET_TITLE) return resp['value'] if resp['value'] is not None else ""@propertydef current_url(self): """ Gets the URL of the current page.
:Usage: driver.current_url """ return self.execute(Command.GET_CURRENT_URL)['value']@propertydef page_source(self): """ Gets the source of the current page.
:Usage: driver.page_source """ return self.execute(Command.GET_PAGE_SOURCE)['value']
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以上并没有列全，我们简单的尝试以上函数的使用方法，使用方法在函数中已经说明。尝试获取 title（标题）、currenturl（当前 url）、pagesource（网页源代码）：
from selenium import webdriverdriver = webdriver.Chrome()driver.get("http://www.csdn.net")print(driver.title)print(driver.current_url)print('作者博客：https://blog.csdn.net/A757291228')#支持原创，转载请贴上原文链接# print(driver.page_source)
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结果成功获取到网页标题以及当前网址：
试试 page_source：
from selenium import webdriverdriver = webdriver.Chrome()driver.get("http://www.csdn.net")print(driver.title)print(driver.current_url)print('作者博客：https://blog.csdn.net/A757291228')#支持原创，转载请贴上链接print(driver.page_source)
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成功获取：
原创不易，看到这里点个赞支持一下呗！谢谢
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