写在前面

感谢@Cstances学长的帮助。

贴代码：

import re
import os
import requests
from bs4 import BeautifulSoup

'''
第一步：获取单页图片的链接
第二步：获取页数的数字
第三步：获取所有图片的链接
第四步：保存图片
'''

def get_images(url):
    """获取单页图片链接"""
    headers = {'User-Agent':'Mozilla/5.0 (Linux; Android 6.0; Nexus 5 Build/MRA58N) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/60.0.3112.90 Mobile Safari/537.36'}
    html = requests.get(url, headers=headers)
    html.encoding = 'utf-8'
    soup = BeautifulSoup(html.text, 'lxml')

    single_page_imgurls = [] # 用于保存当前页的图片链接
    div_a = soup.find('ol' ,{'class':'commentlist'}).find_all('a', href=re.compile(r'//(.*?\.jpg)')) #获取a标签
    for url in div_a:
        single_page_imgurls.append('http:' + url['href'])
    return single_page_imgurls

def get_pages(url):
    """获取首页 page number"""
    headers = {'User-Agent':'Mozilla/5.0 (Linux; Android 6.0; Nexus 5 Build/MRA58N) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/60.0.3112.90 Mobile Safari/537.36'}
    html = requests.get(url, headers=headers)
    html.encoding = 'utf-8'
    soup = BeautifulSoup(html.text, 'lxml')

    pattern = re.compile(r'<span class="current-comment-page">\[(.*)\]</span>')
    pagesNow = pattern.search(str(soup)).groups()[0]
    return pagesNow

def get_all_images(max_pages):
    """获取所有的图片链接"""
    all_images_url = [] #保存所有图片的链接
    page_num = int(get_pages('http://jandan.net/ooxx'))
    for page in range(page_num, page_num-max_pages, -1): #图片是倒着来取的
        url = 'http://jandan.net/ooxx/page-' + str(page) + '#comments'
        all_images_url.extend(get_images(url))#把单页的图片链接加到all_images_url里
    return all_images_url

def save_images(url, dir_name='ooxx'):
    if not os.path.exists(dir_name):
        os.mkdir(dir_name)
    with open(dir_name+os.sep+url.split('/')[-1], 'wb') as fp:
        fp.write(requests.get(url).content)



def main():
    endpage = int(input('请输入要下载的页数：'))
    all_images_url = get_all_images(endpage)
    for img_url in all_images_url:
        save_images(img_url)

if __name__ == '__main__':
    main()

效果图