很多 case 在运行时都会出现页面还没加载完成，但是脚本已经跑完，并且报未找到元素
这是就需要增加判断，在预定的时间内如果页面显示了某元素后再让脚本继续执行，则为判断元素是否可见或者说页面是否显示了某元素
以百度首页，搜素框为例：
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) 只是判断元素是否可见，若果这样写明显存在不合理的地方。如果代码运行很快，页面还未加载完就会出现该元素可见找不到。
所以通常需要结合 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 类，他需要传入driver，超时时间timeout，而 unit 只需要传入定位元素，如下代码 WebDriverWait 类所示
所以在使用 WebDriverWait 时需要对元素定位使用 By 定位，剔除通过 driver 再定位的方法，如上代码所示
WebDriverWait 类
# Licensed to the Software Freedom Conservancy (SFC) under one
# or more contributor license agreements. See the NOTICE file
# distributed with this work for additional information
# regarding copyright ownership. The SFC licenses this file
# to you under the Apache License, Version 2.0 (the
# "License"); you may not use this file except in compliance
# with the License. You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing,
# software distributed under the License is distributed on an
# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
# KIND, either express or implied. See the License for the
# specific language governing permissions and limitations
# under the License. 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)
元素是否可见的方法
visibility_of_element_located : 判断某个元素是否可见
invisibility_of_element_located : 判断某个元素是否不存在或不可见
visibility_of : 判断元素是否可见，通过 driver 查找元素，如：EC.visibility_of(driver.find_element_by_id('kw'))
visibility_of_all_elements_located() ：判断定位的所有元素都存在于DOM树中并且可见，可存在则以list形式返回
visibility_of_any_elements_located() ： 判断定位的所有元素中，至少有一个存在于DOM树中并且可见，list形式返回存在的元素