Selenium has three waiting methods (forced waiting, implicit waiting, and display waiting)

1、 Mandatory waiting （sleep）

from time import sleep
sleep(3)  #  Mandatory waiting 3 second 

shortcoming ： because Web The speed of loading depends on the hardware being tested 、 Network speed 、 Server response time and other factors . If the waiting time is too long , It's easy to waste time , If the waiting time is too short, it may result in web You haven't loaded the required location yet element, And an error is reported .
Because the waiting time cannot be determined , Use too much sleep Will affect the running speed , Greatly reduce efficiency , Therefore, it is recommended to use less forced waiting in the test .

2、 An implicit wait ( implicitly_wait)

#  An implicit wait 10s
driver.implicitly_wait(10) 

brief introduction ： Implicit waiting is global and targeted at all elements , Set the waiting time such as 10 second , If 10 Seconds to appear , Then continue down , Otherwise, throw it out of order . It can be understood that 10 Within seconds , Keep refreshing to see if the element is loaded .
Use scenarios ： Implicit wait only needs to be declared once , It is usually declared after opening the browser . After the statement to the whole drvier The life cycle of , There is no need to repeat the statement . There is a problem with implicit waiting , That is, the program will wait for the whole page to load , In other words, generally you see that the small circle in the browser tab bar doesn't rotate any more , To take the next step , But sometimes the elements the page wants are already loaded , But because of the individual js Things like that are very slow , You still have to wait until the page is complete before you go to the next step .

3、 According to wait ( expected_conditions)

brief introduction ： Show that waiting is for an element alone , Set a waiting time such as 5 second , every other 0.5 Check whether it appears every second , If in 5 Seconds before any time , Then continue down , Generally, it is necessary to cooperate with this kind of until() and until_not() Methods used together , Until the set maximum time is exceeded , Then throw a timeout error TimeoutException, Here are some of the most common methods ：

1. Judge element Whether or not visible ：visibility_of_element_located(locator) （ Visible represents element Non hidden , also element Neither width nor height is equal to 0）

from selenium.webdriver.support import expected_conditions as EC
from selenium.webdriver.support.wait import WebDriverWait
from selenium.webdriver.common.by import By
#  Example 
target = EC.visibility_of_element_located(By.ID,'user')

#  coordination until() Use （ Wait for the element to be visible ）
# 5 Express   Maximum timeout , Default in seconds ; 1 Indicates the interval step of detection , While waiting , Every once in a while ( Default 0.5 second ), call until or until_not The method in , Until it comes back True or False.
WebDriverWait(driver, 5, 1).until(EC.visibility_of_element_located(By.ID,'user'))
#  coordination until_not() Use （ Wait for the element to be invisible ）
WebDriverWait(driver, 5, 1).until_not(EC.visibility_of_element_located(By.ID,'user'))

#  Encapsulated as a function in a class 
    def wait_eleLocated(self, loc, timeout=30, poll_frequency=0.5, model=None):
        """
        :param loc: Element location expression ; A tuple type , The way of expression ( Element location type , Element positioning method ), Example ：(By.ID, "kw")
        :param timeout: Timeout time 
        :param poll_frequency: Polling frequency 
        :param model: Wait for failure , Screenshot operation , The function annotation to be expressed in the picture file 
        :return:None
        """
        self.logger.info(f' wait for "{model}" Elements , Positioning mode :{loc}')
        try:
            start = datetime.now()
            WebDriverWait(self.driver, timeout, poll_frequency).until(EC.visibility_of_element_located(loc))
            end = datetime.now()
            self.logger.info(f' wait for "{model}" Duration :{end - start}')
        except TimeoutException:
            self.logger.exception(f' wait for "{model}" Element failed , Positioning mode :{loc}')
            #  Screenshot 
            self.save_webImgs(f" Waiting elements [{model}] Something unusual happened ")
            raise

2. Judge a certain element Whether it is loaded into dom Trees ：presence_of_element_located(locator) （ It doesn't mean that element It must be visible ）

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

target = EC.presence_of_element_located(By.ID,'user')

3. Judge a certain element Is visible and clickable in ：element_to_be_clickable(locator)

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

target = EC.element_to_be_clickable(By.ID,'user')

4. Judge a certain element Is it selected ：element_to_be_selected(element) （ Usually used in drop-down list ）

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

element = driver.find_element_by_class_name('selector')
EC.element_to_be_selected(element)

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