Selenium2+python自动化38-显式等待（WebDriverWait）
前言：
在脚本中加入太多的sleep后会影响脚本的执行速度，虽然implicitly_wait()这种方法隐式等待方法一定程度上节省了很多时间。
但是一旦页面上某些js无法加载出来（其实界面元素经出来了），左上角那个图标一直转圈，这时候会一直等待的。
一、参数解释
1.这里主要有三个参数：
class WebDriverWait(object):driver, timeout, poll_frequency
2.driver:返回浏览器的一个实例，这个不用多说
3.timeout：超时的总时长
4.poll_frequency：循环去查询的间隙时间，默认0.5秒
以下是源码的解释文档（案例一个是元素出现，一个是元素消失）
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())
"""
二、元素出现：until()
1.until里面有个lambda函数，这个语法看python文档吧
2.以百度输入框为例
三、元素消失：until_not（）
1.判断元素是否消失，是返回Ture,否返回False
备注：此方法未调好，暂时放这
四、参考代码：
# coding:utf-8
from selenium import webdriver
from selenium.webdriver.support.wait import WebDriverWait
driver = webdriver.Firefox()
driver.get("http://www.baidu.com")
# 等待时长10秒，默认0.5秒询问一次
WebDriverWait(driver, 10).until(lambda x: x.find_element_by_id("kw")).send_keys("yoyo")
# 判断id为kw元素是否消失
is_disappeared = WebDriverWait(driver, 10, 1).\
until_not(lambda x: x.find_element_by_id("kw").is_displayed())
print is_disappeared
五、WebDriverWait源码
1.WebDriverWait主要提供了两个方法，一个是until(),另外一个是until_not(）
以下是源码的注释，有兴趣的小伙伴可以看下
# 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)
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