selenium源码分析

import warnings

from selenium.webdriver.remote.webdriver import WebDriver as RemoteWebDriver
from .remote_connection import ChromeRemoteConnection
from .service import Service
from .options import Options

#这个就是入口文件实例化chrome
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
    """
    #入口函数， chromedriver是谷歌浏览器接口，其实就是对谷歌驱动做了一次封装
    #谷歌提供的驱动其实就相当于一个服务器，使用命令就可以调用，而selenium是对驱动做了封装
    #使得编写python脚本就可以调用驱动。类似于postman作用
    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.
        """
        #如果有参数，赋值
        if chrome_options:
            warnings.warn('use options instead of chrome_options',
                          DeprecationWarning, stacklevel=2)
            options = chrome_options
        #如果实例化webdriver没有传参的话，那么给他一个默认值
        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())
        #service_args用来给chromedriver加参数的，比如说一些chromedriver运行日志存放路径
        #获取了一个随机端口并产生一个service实例化
        self.service = Service(
            executable_path,
            port=port,
            service_args=service_args,
            log_path=service_log_path)
        self.service.start()

        try:
            #发送命令，请求长连接
            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):
        """
        Gets Chrome network emulation settings.

        :Returns:
            A dict. For example:

            {'latency': 4, 'download_throughput': 2, 'upload_throughput': 2,
            'offline': False}

        """
        return self.execute("getNetworkConditions")['value']

    def set_network_conditions(self, **network_conditions):
        """
        Sets Chrome network emulation settings.

        :Args:
         - network_conditions: A dict with conditions specification.

        :Usage:
            driver.set_network_conditions(
                offline=False,
                latency=5,  # additional latency (ms)
                download_throughput=500 * 1024,  # maximal throughput
                upload_throughput=500 * 1024)  # maximal throughput

            Note: 'throughput' can be used to set both (for download and upload).
        """
        self.execute("setNetworkConditions", {
            'network_conditions': network_conditions
        })

    def execute_cdp_cmd(self, cmd, cmd_args):
        """
        Execute Chrome Devtools Protocol command and get returned result

        The command and command args should follow chrome devtools protocol domains/commands, refer to link
        https://chromedevtools.github.io/devtools-protocol/

        :Args:
         - cmd: A str, command name
         - cmd_args: A dict, command args. empty dict {} if there is no command args

        :Usage:
            driver.execute_cdp_cmd('Network.getResponseBody', {'requestId': requestId})

        :Returns:
            A dict, empty dict {} if there is no result to return.
            For example to getResponseBody:

            {'base64Encoded': False, 'body': 'response body string'}

        """
        return self.execute("executeCdpCommand", {'cmd': cmd, 'params': cmd_args})['value']

    def quit(self):
        """
        Closes the browser and shuts down the ChromeDriver executable
        that is started when starting the ChromeDriver
        """
        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()