工具介绍
Selenium是一个用于Web应用程序自动化测试工具。Selenium测试直接运行在浏览器中，就像真正的用户在操作一样。支持的浏览器包括IE（7, 8, 9, 10, 11），Mozilla Firefox，Safari，Google Chrome，Opera等。
主要功能包括：①测试与浏览器的兼容性 ②测试系统功能
通过源码看原理
python + selenium 安装
- 首先安装python3。去官网下载所需版本、位数的python安装程序
- 将python安装好后，设置一下python的环境变量，这样在终端里能方便使用python
- 安装selenium的python库，可以直接通过
pip install seleinum安装 - 下载对应版本的selenium浏览器驱动，下载地址:
python示例
简单示例：1
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21# -*- coding: UTF8 -*-
"""
File Name： selenium_test.py
Author : jynne
Date： 2019/04/01
"""
import time
from selenium import webdriver
from selenium.webdriver.common.keys import Keys
browser = webdriver.Chrome(executable_path="./chromedriver") # mac上
# 由于我将chromedriver和脚本放在同级目录，没有写入环境变量，所以这里需要传入driver的路径
browser.get('http://www.baidu.com') # 打开百度首页
assert '百度' in browser.title
elem = browser.find_element_by_name('wd') # 搜索框
elem.send_keys('seleniumhq' + Keys.RETURN) # 搜索
time.sleep(10)
browser.quit()
以上是一个简单的selenium在python中的使用示例，效果是 打开chrome浏览器，并打开百度首页，输入seleniumhq并回车搜索。
原理分析
- webdriver.Chrome(executable_path=”./chromedriver”)
调试进函数内部：1
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140"""
***\Lib\site-packages\selenium\webdriver\chrome\webdriver.py
"""
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):
"""
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()
webdriver.Chrome()定位到__init__(),为什类名不是Chrome？
因为在/site-packages/selenium/webdriver/__init__.py中，
通过源码可以看见（上述代码的12-64行），webdriver.Chrome()主要是创建了一个Service，并且启动Service，然后创建RemoteWebDriver。
(1) self.service = Service()
进入源码：site-packages/selenium/webdriver/chrome/service.py
继续通过父类创建Service：
site-packages/selenium/webdriver/common/service.py
作用就是创建了一个Service
(2) service.start()1
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47""" site-packages/selenium/webdriver/common/service.py """
class Service(object):
""" ………… """
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)
本质是执行了一个cmd命令: ./chromedriver --port=53393'，作用是启动chromedriver，端口号是53393
(3) RemoteWebDriver.init()
首先看一下传入的参数：1
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6RemoteWebDriver.__init__(
self,
command_executor=ChromeRemoteConnection(
remote_server_addr=self.service.service_url,
keep_alive=keep_alive),
desired_capabilities=desired_capabilities)
command_executor的值是一个ChromeRemoteConnection实例，
实际上就是一个RemoteConnection，和Remote WebDriver server进行通信的连接，所有的命令存在self._command中。
再看RemoteWebDriver.init()的源码：site-packages/selenium/webdriver/remote/webdriver.py1
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65class WebDriver(object):
"""
Controls a browser by sending commands to a remote server.
This server is expected to be running the WebDriver wire protocol
as defined at
https://github.com/SeleniumHQ/selenium/wiki/JsonWireProtocol
:Attributes:
- session_id - String ID of the browser session started and controlled by this WebDriver.
- capabilities - Dictionaty of effective capabilities of this browser session as returned
by the remote server. See https://github.com/SeleniumHQ/selenium/wiki/DesiredCapabilities
- command_executor - remote_connection.RemoteConnection object used to execute commands.
- error_handler - errorhandler.ErrorHandler object used to handle errors.
"""
_web_element_cls = WebElement
def __init__(self, command_executor='http://127.0.0.1:4444/wd/hub',
desired_capabilities=None, browser_profile=None, proxy=None,
keep_alive=False, file_detector=None, options=None):
"""
Create a new driver that will issue commands using the wire protocol.
:Args:
- command_executor - Either a string representing URL of the remote server or a custom
remote_connection.RemoteConnection object. Defaults to 'http://127.0.0.1:4444/wd/hub'.
- desired_capabilities - A dictionary of capabilities to request when
starting the browser session. Required parameter.
- browser_profile - A selenium.webdriver.firefox.firefox_profile.FirefoxProfile object.
Only used if Firefox is requested. Optional.
- proxy - A selenium.webdriver.common.proxy.Proxy object. The browser session will
be started with given proxy settings, if possible. Optional.
- keep_alive - Whether to configure remote_connection.RemoteConnection to use
HTTP keep-alive. Defaults to False.
- file_detector - Pass custom file detector object during instantiation. If None,
then default LocalFileDetector() will be used.
- options - instance of a driver options.Options class
"""
capabilities = {}
if options is not None:
capabilities = options.to_capabilities()
if desired_capabilities is not None:
if not isinstance(desired_capabilities, dict):
raise WebDriverException("Desired Capabilities must be a dictionary")
else:
capabilities.update(desired_capabilities)
if proxy is not None:
warnings.warn("Please use FirefoxOptions to set proxy",
DeprecationWarning, stacklevel=2)
proxy.add_to_capabilities(capabilities)
self.command_executor = command_executor
if type(self.command_executor) is bytes or isinstance(self.command_executor, str):
self.command_executor = RemoteConnection(command_executor, keep_alive=keep_alive)
self._is_remote = True
self.session_id = None
self.capabilities = {}
self.error_handler = ErrorHandler()
self.start_client()
if browser_profile is not None:
warnings.warn("Please use FirefoxOptions to set browser profile",
DeprecationWarning, stacklevel=2)
self.start_session(capabilities, browser_profile)
self._switch_to = SwitchTo(self)
self._mobile = Mobile(self)
self.file_detector = file_detector or LocalFileDetector()
比较关键的是62行的self.start_session(capabilities, browser_profile)，
作用是执行了newSession的命令，发送了一个post请求，参数是json格式的，返回response
当web driver接收到请求后，浏览器驱动程序解析请求，打开浏览器，并获得sessionid，在response中返回
后续再执行各类操作时，都会在请求中拼接上session id