要求：获取下图指定网站的指定数据

空气质量状况报告-中国环境监测总站

输入：用户输入下载时间范围，格式为2022-10

输出：将更新时间在2022年10月1日到31日之间的文件下载到本地目录（可配置），并将下载的标题列表逐行打印在控制台console中

完成标准：

程序正常运行

import requests
from lxml import etree
from urllib.parse import urljoin
from datetime import datetime

def download_files(start_date,end_date):
    headers = {
        "User-Agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/114.0.0.0 Safari/537.36"
    }
    base_url = "http://www.cnemc.cn/jcbg/kqzlzkbg/index"
    page=0
    while True:
        if page==0:
            url=f"{base_url}.shtml"
        else:
            url=f"{base_url}_{page}.shtml"
    # url = "http://www.cnemc.cn/jcbg/kqzlzkbg/index.shtml"
        response = requests.get(url, headers=headers)
        if response.status_code!=200:
            break
        response.encoding = response.apparent_encoding
        page_text = response.text
        html = etree.HTML(page_text)
        divs = html.xpath('//*[@id="contentPageData"]/li')
        for i in divs:

            # 使用 XPath 定位到 <a> 标签并提取文本
            title = i.xpath('.//a/text()')  # 获取第一个匹配元素的文本

            # 使用 XPath 定位到 <span class="txt_time"> 标签并提取文本
            date_str = i.xpath('.//span[@class="txt_time"]/text()')

            if title and date_str:
                title = title[0].strip()
                date = datetime.strptime(date_str[0].strip(),'%Y-%m-%d')
                if start_date <= date <= end_date:
                    a_tag = i.find('.//a')
                    link = a_tag.get('href') if a_tag is not None else None
                    print(f'下载标题：{title}')
                    print(link)
                    base_link='http://www.cnemc.cn/jcbg/kqzlzkbg/'
                    full_link=urljoin(base_link,link)
                    print(full_link)
                    response_son = requests.get(full_link, headers=headers)
                    response_son.encoding = response_son.apparent_encoding
                    page_text_son=response_son.text
                    # print(page_text_son)
                    html_son = etree.HTML(page_text_son)
                    divs_son=html_son.xpath('/html/body/div[1]/div[5]/div/div[1]')[0]
                    # print(divs_son)        #/html/body/div[1]/div[5]/div/div[1]
                    a_tag_son = divs_son.find('.//a')
                    link_file = a_tag_son.get('href') if a_tag_son is not None else None
                    print(link_file)
                    if "http://www.cnemc.cn/" not in link_file:
                        link_file="http://www.cnemc.cn/jcbg/kqzlzkbg/"+str(start_date.year)+str(start_date.month)+'/'+link_file.lstrip('./')
                        print(link_file)
                    file_path=f"./downloads/{title}.pdf"
                    response_file=requests.get(link_file)
                    if response_file.status_code==200:
                        with open(file_path,'wb') as f:
                            f.write(response_file.content)
                        print("文件下载成功，保存至:", file_path)
                    else:
                        print("下载失败，状态码:", response_file.status_code)
        page+=1
if __name__=="__main__":
    start_date=datetime(2016,4,1)
    end_date=datetime(2016,4,30)
    download_files(start_date,end_date)