Selenium2+python自動化38-顯式等待（WebDriverWait）

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前言：

在指令碼中加入太多的sleep後會影響指令碼的執行速度，雖然implicitly_wait()這種方法隱式等待方法一定程度上節省了很多時間。

但是一旦頁面上某些js無法載入出來（其實介面元素經出來了），左上方那個表徵圖一直轉圈，這時候會一直等待的。

一、參數解釋

1.這裡主要有三個參數：

class WebDriverWait(object):driver, timeout, poll_frequency

2.driver:返回瀏覽器的一個執行個體，這個不用多說

3.timeout：逾時的總時間長度

4.poll_frequency：迴圈去查詢的間隙時間，預設0.5秒

以下是源碼的解釋文檔（案例一個是元素出現，一個是元素消失）
    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、元素出現：until()

1.until裡面有個lambda函數，這個文法看python文檔吧

2.以百度輸入框為例

三、元素消失：until_not（）

1.判斷元素是否消失，是返回Ture,否返回False

備忘：此方法未調好，暫時放這

四、參考代碼：

# coding:utf-8
from selenium import webdriver
from selenium.webdriver.support.wait import WebDriverWait

driver = webdriver.Firefox()
driver.get("http://www.baidu.com")
# 等待時間長度10秒，預設0.5秒詢問一次
WebDriverWait(driver, 10).until(lambda x: x.find_element_by_id("kw")).send_keys("yoyo")

# 判斷id為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源碼

1.WebDriverWait主要提供了兩個方法，一個是until(),另外一個是until_not(）

以下是源碼的注釋，有興趣的小夥伴可以看下

# 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)

Selenium2+python自動化38-顯式等待（WebDriverWait）