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web自动化测试页面等待

2021-03-09 23:30:41 作者：互联网

Waits 等待

WebDriver因为是异步触发元素或事件，有些时候脚本可能是间接性的，也有可能是断断续续的；又加浏览器和WebDriver脚本之间的存在竞争条件问题，因此我们需要引入等待包，让脚本运行不会出现阻塞或失败

使用等待时，我们需要引入等待包：

ui和wait里面都有WebDriverWait类，目前两种引包使用都没问题的；区别的话就是：ui模块里面引入的类就是wait下的WebDriverWait类


from selenium.webdriver.support.ui import WebDriverWait


from selenium.webdriver.support.wait import WebDriverWait

三大等待之：显式等待

显式等待部分源码简介：


class WebDriverWait(object):
    def __init__(self, driver, timeout, poll_frequency=POLL_FREQUENCY, 
        self._driver = driver
        self._timeout = timeout
        self._poll = poll_frequency
        # avoid the divide by zero
        if self._poll == 0:
            self._poll = POLL_FREQUENCY
        exceptions = list(IGNORED_EXCEPTIONS)
        if ignored_exceptions is not None:
            try:
                exceptions.extend(iter(ignored_exceptions))
            except TypeError:  # ignored_exceptions is not iterable
                exceptions.append(ignored_exceptions)
        self._ignored_exceptions = tuple(exceptions)

    ...... # 省略的源码

    def until(self, method, message=''):
        """Calls the method provided with the driver as an argument until the \
        return value is not False."""
        screen = None
        stacktrace = None

        end_time = time.time() + self._timeout
        while True:
            try:
                value = method(self._driver)
                if value:
                    return value
            except self._ignored_exceptions as exc:
                screen = getattr(exc, 'screen', None)
                stacktrace = getattr(exc, 'stacktrace', None)
            time.sleep(self._poll)
            if time.time() > end_time:
                break
        raise TimeoutException(message, screen, stacktrace)

driver ：Webdriver的实例(Ie、Firefox、Chrome)
timeout ：设置超时时间
poll_frequency ：休眠轮询时间，默认是0.5秒
ignored_exceptions ：忽略特定的指定的异常

显式等待30秒，找不到元素就会抛出超时信息：


from selenium import webdriver
from selenium.webdriver.support.wait import WebDriverWait

driver = webdriver.Chrome()
driver.get('https://www.baidu.com/')


def waits_data(d):
    return d.find_element_by_xpath("//a[contains(text(),'高级搜索')]")


WebDriverWait(driver, 30).until(waits_data)


F:\virtualEnvironment\venv\Scripts\python.exe F:/git/AuomationTest/AuomationTestProject/webTestAuomation/selenium_waits.py
Traceback (most recent call last):
  File "F:/git/AuomationTest/AuomationTestProject/webTestAuomation/selenium_waits.py", line 19, in <module>
    WebDriverWait(driver, 30).until(waits_data)
  File "F:\virtualEnvironment\venv\lib\site-packages\selenium\webdriver\support\wait.py", line 80, in until
    raise TimeoutException(message, screen, stacktrace)
selenium.common.exceptions.TimeoutException: Message:

您也可以把函数换成匿名函数，但是运行的结果是和上面一致的：


WebDriverWait(driver, 30).until(lambda p: p.find_element_by_xpath("//a[contains(text(),'高级搜索')]"))

WebDriverWait(driver, 30)中的until()方法是可以放判定条件的，满足条件后就不再等待了，until_not()方法是判定不满足条件的，也就是不满足这个条件就不再等待了。

WebDriver也提供了一个期望条件模块 expected_conditions：


from selenium.webdriver.support import expected_conditions

判断元素是否可见，可见指的是元素非隐藏：


from selenium import webdriver
from selenium.webdriver.support.wait import WebDriverWait
from selenium.webdriver.common.by import By
from selenium.webdriver.support import expected_conditions as EC

driver = webdriver.Chrome()
driver.get('https://www.baidu.com/')

WebDriverWait(driver, 30).until(EC.visibility_of_element_located((By.XPATH, "//a[contains(text(),'高级搜索')]")))

alert is present：判断页面上是否存在alert
title contains：判断当前页面的title是否包含预期字符串
title is：判断当前页面的title是否等于预期
frame_to_be_available_and_switch_to_it：检查frame表单是否可切进去。如果可以切进去，就切换到指定的frame框中。

更多的判定条件点击此处进行访问学习

WebDriverWait中忽略异常：

ignored_exceptions传入异常名称，可传多个异常名称，多个时以列表存储即可，异常最好捕获selenium.common.exceptions报出来的，基于BaseException的异常貌忽略不成功


# 捕获单个异常

WebDriverWait(driver, 5, ignored_exceptions='NoSuchElementException').until(EC.visibility_of_element_located((By.XPATH,"//a[contains(text(),'高级搜索')]")))

# 捕获多个异常

WebDriverWait(driver, 5, ignored_exceptions=['TimeoutException', 'NoSuchElementException']).until(EC.visibility_of_element_located((By.XPATH, "//a[contains(text(),'高级搜索')]")))

三大等待之：隐式等待

WebDriver在尝试查找任何元素时会轮询DOM一定时间。当网页上的某些元素无法立即使用且需要一些时间来加载时，需要了隐式等待，默认情况下隐式等待内元素是禁止出现的

注意：请勿混合使用隐式和显式等待，可能导致无法预测等待时间


from selenium import webdriver
from selenium.webdriver.support.wait import WebDriverWait
from selenium.webdriver.common.by import By
from selenium.webdriver.support import expected_conditions as EC

driver = webdriver.Chrome()
driver.implicitly_wait(10)
driver.get('https://www.baidu.com/')
driver.find_element_by_xpath("//a[contains(text(),'高级搜索')]")

设置了driver.implicitly_wait(10)等待10秒，超过10秒等不到就抛异常：


F:\virtualEnvironment\venv\Scripts\python.exe F:/git/AuomationTest/AuomationTestProject/webTestAuomation/selenium_waits.py
Traceback (most recent call last):
  File "F:/git/AuomationTest/AuomationTestProject/webTestAuomation/selenium_waits.py", line 27, in <module>
    driver.find_element_by_xpath("//a[contains(text(),'高级搜索')]")
  File "F:\virtualEnvironment\venv\lib\site-packages\selenium\webdriver\remote\webdriver.py", line 394, in find_element_by_xpath
    return self.find_element(by=By.XPATH, value=xpath)
  File "F:\virtualEnvironment\venv\lib\site-packages\selenium\webdriver\remote\webdriver.py", line 978, in find_element
    'value': value})['value']
  File "F:\virtualEnvironment\venv\lib\site-packages\selenium\webdriver\remote\webdriver.py", line 321, in execute
    self.error_handler.check_response(response)
  File "F:\virtualEnvironment\venv\lib\site-packages\selenium\webdriver\remote\errorhandler.py", line 242, in check_response
    raise exception_class(message, screen, stacktrace)
selenium.common.exceptions.NoSuchElementException: Message: no such element: Unable to locate element: {"method":"xpath","selector":"//a[contains(text(),'高级搜索')]"}
  (Session info: chrome=89.0.4389.72)

三大等待之：强制等待

导入time包，引入seep方法来强制等待，有些时候的页面加载的慢，可以使用这个强制睡眠1-2秒，能保证脚本运行的稳定性


import time
from selenium import webdriver
from selenium.webdriver.support.wait import WebDriverWait
from selenium.webdriver.common.by import By
from selenium.webdriver.support import expected_conditions as EC

driver = webdriver.Chrome()
driver.get('https://www.baidu.com/')
time.sleep(30)
driver.find_element_by_xpath("//a[contains(text(),'高级搜索')]")

time.seep(10)设置了10秒，超过时间没找到就抛异常：


F:\virtualEnvironment\venv\Scripts\python.exe F:/git/AuomationTest/AuomationTestProject/webTestAuomation/selenium_waits.py
Traceback (most recent call last):
  File "F:/git/AuomationTest/AuomationTestProject/webTestAuomation/selenium_waits.py", line 27, in <module>
    driver.find_element_by_xpath("//a[contains(text(),'高级搜索')]")
  File "F:\virtualEnvironment\venv\lib\site-packages\selenium\webdriver\remote\webdriver.py", line 394, in find_element_by_xpath
    return self.find_element(by=By.XPATH, value=xpath)
  File "F:\virtualEnvironment\venv\lib\site-packages\selenium\webdriver\remote\webdriver.py", line 978, in find_element
    'value': value})['value']
  File "F:\virtualEnvironment\venv\lib\site-packages\selenium\webdriver\remote\webdriver.py", line 321, in execute
    self.error_handler.check_response(response)
  File "F:\virtualEnvironment\venv\lib\site-packages\selenium\webdriver\remote\errorhandler.py", line 242, in check_response
    raise exception_class(message, screen, stacktrace)
selenium.common.exceptions.NoSuchElementException: Message: no such element: Unable to locate element: {"method":"xpath","selector":"//a[contains(text(),'高级搜索')]"}
  (Session info: chrome=89.0.4389.72)

以上总结或许能帮助到你，或许帮助不到你，但还是希望能帮助到你，如有疑问、歧义，评论区留言会及时修正发布，谢谢！

未完，待续…
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标签：web,webdriver,selenium,driver,element,自动化,exceptions,import,页面
来源： https://blog.csdn.net/LIFENG0402/article/details/114593219