selenium-判斷元素是否可見（五）

很多 case 在運行時都會出現頁面還沒加載完成，但是腳本已經跑完，並且報未找到元素

這是就需要增加判斷，在預定的時間內如果頁面顯示了某元素后再讓腳本繼續執行，則為判斷元素是否可見或者說頁面是否顯示了某元素

 

以百度首頁，搜素框為例：

from selenium import webdriver
from selenium.webdriver.support import expected_conditions as EC

driver = webdriver.Chrome()
driver.get('https://www.baidu.com/')
baidu_input = driver.find_element_by_id('kw')
EC.visibility_of_element_located(baidu_input)

driver.close()

EC.visibility_of_element_located(baidu_input) 只是判斷元素是否可見，若果這樣寫明顯存在不合理的地方。如果代碼運行很快，頁面還未加載完就會出現該元素可見找不到。
所以通常需要結合 WebDriverWait 一起使用

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

driver = webdriver.Chrome()
driver.get('https://www.baidu.com/')
baidu_input = (By.ID, 'kw')
WebDriverWait(driver,10).until(EC.visibility_of_element_located(baidu_input))

driver.close()

查看 WebDriverWait 類，他需要傳入driver，超時時間timeout，而 unit 只需要傳入定位元素，如下代碼 WebDriverWait 類所示

所以在使用 WebDriverWait 時需要對元素定位使用 By 定位，剔除通過 driver 再定位的方法，如上代碼所示

WebDriverWait 類

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import time
from selenium.common.exceptions import NoSuchElementException
from selenium.common.exceptions import TimeoutException

POLL_FREQUENCY = 0.5  # How long to sleep inbetween calls to the method
IGNORED_EXCEPTIONS = (NoSuchElementException,)  # exceptions ignored during calls to the method


class WebDriverWait(object):
    def __init__(self, driver, timeout, poll_frequency=POLL_FREQUENCY, ignored_exceptions=None):
        """Constructor, takes a WebDriver instance and timeout in seconds.

           :Args:
            - driver - Instance of WebDriver (Ie, Firefox, Chrome or Remote)
            - timeout - Number of seconds before timing out
            - poll_frequency - sleep interval between calls
              By default, it is 0.5 second.
            - ignored_exceptions - iterable structure of exception classes ignored during calls.
              By default, it contains NoSuchElementException only.

           Example:
            from selenium.webdriver.support.ui import WebDriverWait \n
            element = WebDriverWait(driver, 10).until(lambda x: x.find_element_by_id("someId")) \n
            is_disappeared = WebDriverWait(driver, 30, 1, (ElementNotVisibleException)).\ \n
                        until_not(lambda x: x.find_element_by_id("someId").is_displayed())
        """
        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)

    def __repr__(self):
        return '<{0.__module__}.{0.__name__} (session="{1}")>'.format(
            type(self), self._driver.session_id)

    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)

    def until_not(self, method, message=''):
        """Calls the method provided with the driver as an argument until the \
        return value is False."""
        end_time = time.time() + self._timeout
        while True:
            try:
                value = method(self._driver)
                if not value:
                    return value
            except self._ignored_exceptions:
                return True
            time.sleep(self._poll)
            if time.time() > end_time:
                break
        raise TimeoutException(message)

 

元素是否可見的方法

　　visibility_of_element_located : 判斷某個元素是否可見
　　invisibility_of_element_located : 判斷某個元素是否不存在或不可見
　　visibility_of : 判斷元素是否可見，通過 driver 查找元素，如：EC.visibility_of(driver.find_element_by_id('kw'))
　　visibility_of_all_elements_located() ：判斷定位的所有元素都存在於DOM樹中並且可見，可存在則以list形式返回
　　visibility_of_any_elements_located() ： 判斷定位的所有元素中，至少有一個存在於DOM樹中並且可見，list形式返回存在的元素