使用python写出上列代码

当然，以下是使用Python编写的示例代码，它包含了上述步骤的主要部分。请注意，实际的实施可能会因为网站结构和反爬策略的不同而有所调整。这里假设我们使用了`beautifulsoup4`、`requests`以及`pyppeteer`（对于处理JavaScript加载的页面）作为基础库。

# 导入所需的库
import os
import re
import requests
from bs4 import BeautifulSoup
from urllib.parse import urljoin
from pyppeteer import launch

# 配置选项（这里仅示例）
base_url = 'https://www.example.com'
output_dir = 'downloads'

# 函数用于下载PDF
def download_pdf(url):
    browser = launch()
    page = browser.newPage()
    page.goto(url)
    pdf_data = page.evaluate('window.navigator.userAgent')
    browser.close()

    # 如果是JavaScript加载的PDF，替换这里的逻辑
    if 'PDF.js' in pdf_data:
        # 使用pdfjs-dist库下载
        pass
    else:
        file_path = os.path.join(output_dir, url.split('/')[-1])
        with open(file_path, 'wb') as f:
            f.write(requests.get(url).content)

# 主函数
def crawl_and_download():
    target_url = base_url  # 初始抓取页面 URL
    while True:
        response = requests.get(target_url)
        soup = BeautifulSoup(response.text, 'html.parser')

        # 解析PDF链接
        pdf_links = [urljoin(base_url, a['href']) for a in soup.select('a[href$=".pdf"]')]
        
        for link in pdf_links:
            # 检查是否已存在
            if not os.path.exists(os.path.join(output_dir, link.split('/')[-1])):
                try:
                    download_pdf(link)
                    print(f'Downloaded {link}')
                except Exception as e:
                    print(f'Error downloading {link}: {e}')

        # 获取下一页链接（如果有的话）
        next_page_link = soup.select_one('div.pagination a.next')
        if next_page_link is None:
            break
        target_url = urljoin(base_url, next_page_link['href'])

crawl_and_download()

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