Selenium waiting mode

summary

stay selenium in , Waiting refers to waiting for the completion of the previous task before executing the next task , Before the previous task is completed , The latter task will always be in a blocking state , It is somewhat similar to transactions in a database . such as , Before locating the element, you need to load DOM.selenium There are three ways to wait ： According to wait 、 An implicit wait 、 Smooth waiting .

The way

According to wait

WebDriverWait(driver, timeout).until(method, message)

Show waiting is selenium The imperative process language that customers can use . They allow your code to pause program execution , Or freeze threads , Until the conditions for passing are met . This condition will always be called at a certain frequency , Until the waiting times out . This means that as long as the condition returns a false value , It will keep trying and waiting . This method is also the most commonly used method .

from selenium import webdriver
from selenium.webdriver.common.by import By
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions

driver = webdriver.Chrome()
driver.get("http://www.example.com")
#  Set implicit wait 
# locator It can be tuples (), aggregate {}, Tabular form 
#  function presence_of_element_located Indicates the  DOM  Whether there is an element on 
#  If html There is no label in p The elements of , Then wait for three seconds and throw an exception 
WebDriverWait(driver, timeout=3).until(expected_conditions.presence_of_element_located({By.TAG_NAME, "p"}))
#  If html There are tags in p The elements of , Then find this element 
element = driver.find_element(By.TAG_NAME, "p")

An implicit wait

driver.implicitly_wait(time_to_wait)

An implicit wait ,WebDriver Poll for a certain amount of time when trying to find any element DOM. If the element doesn't exist , An exception will be thrown after the set time . It is useful when some elements on a web page are not immediately available and take some time to load .

Implicit waiting is telling WebDriver If you poll for one or more elements that are not immediately available DOM A span . The default setting is 0, Disable . Once set up , Implicit waiting is set as the life cycle of the session . in other words , After setting the implicit wait , When performing any operation, such as finding elements , There is a certain time limit , If it goes beyond that time , Will throw an exception .

from selenium import webdriver
from selenium.webdriver.common.by import By

driver = webdriver.Chrome()
#  Set implicit wait , The waiting time is 5 second 
driver.implicitly_wait(5)
#  After setting the implicit wait , If 5 The target is not obtained within seconds DOM, Throw an exception 
driver.get("http://www.example.com")
#  After setting the implicit wait , If 5 No element was obtained within seconds a, Throw an exception 
element = driver.find_element(By.TAG_NAME, "a")

Smooth waiting

WebDriverWait(driver, timeout, poll_frequency, ignored_exceptions).until(method, message)

The fluent wait instance defines the maximum amount of time for the wait condition , And the frequency of the inspection conditions . Users can configure waiting to ignore specific types of exceptions when waiting , For example, when searching for elements on the page NoSuchElementException.

from selenium import webdriver
from selenium.common import ElementNotVisibleException, ElementNotSelectableException
from selenium.webdriver.common.by import By
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions

driver = webdriver.Chrome()
driver.get("http://www.example.com")
#  Set smooth waiting 
#  The timeout is 10 second , every other 1 Seconds to check whether ElementNotVisibleException,ElementNotSelectableException These two exceptions , If these two exceptions occur , Ignore it 
wait = WebDriverWait(driver, timeout=10, poll_frequency=1, ignored_exceptions=[ElementNotVisibleException,
                                                                               ElementNotSelectableException])
wait.until(expected_conditions.element_to_be_clickable((By.TAG_NAME, "h")))
element = driver.find_element(By.TAG_NAME, "p")

Because it must be synchronized DOM And instructions are quite common , So most clients also come with a set of predefined waiting conditions . seeing the name of a thing one thinks of its function , They are predefined conditions for frequent wait operations . Here are some optional Waiting conditions ：