Python Selenium 設定元素等待的三種方式
Selenium 設定元素等待的三種方式
1. sleep 強制等待
2. implicitly_wait() 隱性等待
3. WebDriverWait()顯示等待
三種方式的優缺點
1. sleep 強制等待
from selenium import webdriver from time import sleep driver = webdriver.Chrome() sleep(2) #設定等待2秒鐘 driver.get('http://www.baidu.com')
優點:
程式碼簡介,簡單明瞭
缺點:
如果設定sleep等待時間過短,元素還沒加載出來,程式報錯,sleep設定等待時間過長,元素早就加載出來了,程式還在等待,浪費是時間,影響程式碼整體的執行效率
個人看法:
簡單粗暴,根據網站的響應速度和自己的網速來設定合理的休眠時間
2. implicitly_wait() 隱性等待
from selenium import webdriver from time import sleep driver = webdriver.Chrome() driver.implicitly_wait(20) #設定等待20秒鐘 driver.get('http://www.baidu.com')
優點:
1.程式碼簡介
2.在程式碼前部分加implicitly_wait(10) ,整個的程式執行過程中都會有效(作用於全域性,直接在初始化driver的後面加,後面的程式碼都會受影響),都會等待元素載入完成
缺點:
1. 非要載入到整個頁面才執行程式碼,這樣影響程式碼的執行效率,一般情況下,我們想要的結果是隻需載入到了我要定位的元素就執行程式碼,不需要等待整個頁面的完全加載出來再執行程式碼。
個人看法:
1.不適合用在資料在ajax的網站中,比如翻頁什麼的,某個元素一直存在,但是資料一直在變,這樣的話只要加載出來第一頁,後面翻頁的資料全部會和第一頁的資料相同,因為程式碼判斷了這個元素已經被加載出來了,不會等ajax去載入
3. WebDriverWait()顯示等待
from selenium import webdriver from selenium.webdriver.support import expected_conditions as EC from selenium.webdriver.support.ui import WebDriverWait #WebDriverWait注意大小寫 from selenium.webdriver.common.by import By driver = webdriver.Chrome() driver.get('http://www.baidu.com') try: element = WebDriverWait(driver,10).until(EC.presence_of_element_located((By.ID,'kw'))) element.send_keys('123') driver.find_element_by_id('su').click() except Exception as message: print('元素定位報錯%s'%message) finally: pass
優點:
程式碼執行效率快。無需等待整個頁面載入完成,只需載入到你要定位的元素就可以執行程式碼。是最智慧的設定元素等待的方式。
缺點:
1.要匯入from selenium.webdriver.support import expected_conditions as EC
from selenium.webdriver.support.ui import WebDriverWait from selenium.webdriver.common.by import By
必須要匯入以上3個包,導包路徑相當的複雜,囉嗦而且麻煩
2.寫等待時間的程式碼也是複雜。步驟稍微有點多。
element=WebDriverWait(driver,‘kw'))) element.send_keys(‘123')
個人看法: 相比於兩種,這種方式可以算的上好的了,但是就是麻煩,寫的程式碼太多,使用的話可以和第一種方式sleep混合使用,不過我還是喜歡用sleep,本身使用selenium就是沒辦法破開網站,或者使用selenium比直接破解的方式更好才使用這種,我個人是能不用就不用,抓取速度太慢了。
附上我抓取一個網站的程式碼,這網站作者的成果抓不到,只好用這種方式來抓了:
from selenium import webdriver import time from lxml.html import etree import copy import json from selenium.webdriver.common.by import By from selenium.webdriver.support.ui import WebDriverWait from selenium.webdriver.support import expected_conditions as EC def getAuthors(): j1 = set() f = open('Author.json','r',encoding='utf-8') data = f.read() data_list = data.split('\n') for dt in data_list: j1.add(dt) f.close() print('j1= ',len(j1)) j2 = set() f1 = open('yzq.json',encoding='utf-8') data1 = f1.read() data_list1 = data1.split('\n') for dt in data_list1: j2.add(dt) print('j2= ',len(j2)) countSet = j1 - j2 print('countset= ',len(countSet)) AuthorsData = [] for dt in countSet: dt_json = json.loads(dt) if int(dt_json["成果"]) > 0: AuthorsData.append(dt_json) # dt = {'img': 'https://www.scholarmate.com/avatars/99/92/62/37572.jpg','name': '吳偉',# 'url': 'https://www.scholarmate.com/P/aeiUZr','org': '復旦大學,教授','專案': 20,'成果': 234,'H指數': '24'} print('AuthorData= ',len(AuthorsData)) return AuthorsData def parseHtml(html,i): temp_list = [] html_data = etree.HTML(html) project_html = html_data.xpath('//div[@class="pub-idx__main"]') for p in project_html: # pro_name = p.xpath('./div[@class="pub-idx__main_title"]/a/@title')[0] pro_name = p.xpath('.//a/@title')[0].strip().replace(r'\xa0','') # pro_url = p.xpath('./div[@class="pub-idx__main_title"]/a/@href')[0] pro_url = p.xpath('.//a/@href')[0] pro_author = p.xpath('./div[2]/@title')[0].strip().replace('\xa0','') # pro_author = p.xpath('.//div[@class="pub-idx__main_author"]/@title') pro_inst = p.xpath('./div[3]/@title')[0] temp_dict = { 'num': i,'pro_name': pro_name,'pro_url': pro_url,'pro_author': pro_author,'pro_inst': pro_inst } temp_list.append(copy.deepcopy(temp_dict)) return temp_list def parseData(author_data): try: url = author_data['url'] ach_num = int(author_data['成果']) pages = ach_num // 10 pages_ys = ach_num % 10 if pages_ys > 0: pages += 1 driver = webdriver.Chrome() # driver.implicitly_wait(10) driver.get(url) psn_data = [] for i in range(1,pages+1): if i == 1: # 防止抓取到半路的時候頁面沒有響應,這部分資料就直接扔掉 try: # time.sleep(2) driver.find_element_by_xpath('//*[@id="pubTab"]').click() # time.sleep(3) # 有以下這些選擇 # WebDriverWait(driver,5).until(EC.presence_of_element_located((By.ID,'pub-idx__main'))) # WebDriverWait(driver,5).until(EC.presence_of_element_located((By.CLASS_NAME,5).until(EC.presence_of_element_located((By.CSS_SELECTOR,'.//pub-idx__main'))) # 這個也不適合這個網站,還是會抓到重複的 WebDriverWait(driver,5).until(EC.presence_of_element_located((By.XPATH,'//div[@class="pub-idx__main"]'))) html = driver.page_source temp_dict = parseHtml(html,i) psn_data.append(copy.deepcopy(temp_dict)) except: import traceback print(traceback.print_exc()) pass else: # driver.find_element_by_xpath('//*[@id="pubTab"]').click() # 將頁面拉到底部 try: js = "var q=document.documentElement.scrollTop=100000" driver.execute_script(js) # time.sleep(1) driver.find_element_by_xpath('//div[@class="pagination__pages_next"]').click() # time.sleep(2) WebDriverWait(driver,i) psn_data.append(copy.deepcopy(temp_dict)) except: pass driver.close() psn_data = { 'init_data': author_data,'psn_data': psn_data } print(psn_data) psn_data_string = json.dumps(psn_data,ensure_ascii=False) with open('data.json','a+',encoding='utf-8') as f: f.write('{}\n'.format(psn_data_string)) author_data_string = json.dumps(author_data,ensure_ascii=False) with open('yzq.json',encoding='utf-8') as f: f.write('{}\n'.format(author_data_string)) except: pass # import traceback # print(traceback.print_exc()) # au_strign = json.dumps(author_data,ensure_ascii=False) # author_data_string = json.dumps(au_strign,ensure_ascii=False) # with open('error.json',encoding='utf-8') as f: # f.write('{}\n'.format(author_data_string)) def main(): # authors的值:給出三條 # {"img": "https://www.scholarmate.com/avatars/e4/fe/1e/1000002077830.png?A=DMkT","name": "胡婷",# "url": "https://www.scholarmate.com/P/QFFbae","org": "四川大學,主治醫師","專案": "0","成果": "11","H指數": "0"} # {"img": "https://www.scholarmate.com/avatars/01/ea/59/1000002180047.png?A=DVUy","name": "白曉涓",# "url": "https://www.scholarmate.com/P/73me22","org": "","專案": "6","成果": "8","H指數": "0"} # {"img": "https://www.scholarmate.com/avatars/fe/0d/89/1000000732306.png?A=D65r","name": "原鵬飛",# "url": "https://www.scholarmate.com/P/77nIFr","org": "國家統計局統計科學研究所,副研究員","成果": "90","H指數": "0"} AuthorsData = getAuthors() for authors in AuthorsData: print('author= ',authors) parseData(authors) if __name__ == '__main__': main()
友情連結:
https://www.cnblogs.com/zhaof/p/6953241.html
https://blog.csdn.net/xiezhiming1234/article/details/83865314
https://www.cnblogs.com/April-Chou-HelloWorld/p/8855760.html
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