import urllib.request# url request
import re      # regular expression
import os      # dirs
import time
'''
url 下载网址
pattern 正则化的匹配关键词
Directory 下载目录
def BatchDownload(url,pattern,Directory):
   
  # 拉动请求，模拟成浏览器去访问网站->跳过反爬虫机制
  headers = {'User-Agent', 'Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.186 Safari/537.36'}
  opener = urllib.request.build_opener()
  opener.addheaders = [headers]
  # 获取网页内容
  content = opener.open(url).read().decode('utf8')
  # 构造正则表达式，从content中匹配关键词pattern
  raw_hrefs = re.findall(pattern, content, 0)
  # set函数消除重复元素
  hset = set(raw_hrefs)
     
  # 下载链接
  for href in hset:
    # 之所以if else 是为了区别只有一个链接的特别情况
    if(len(hset)>1):
      link = url + href[0]
      filename = os.path.join(Directory, href[0])
      print("正在下载",filename)
      urllib.request.urlretrieve(link, filename)
      print("成功下载！")
    else:
      link = url +href
      filename = os.path.join(Directory, href)
       
    # 无sleep间隔，网站认定这种行为是攻击，反反爬虫
    time.sleep(1)
 
#BatchDownload('https://www1.ncdc.noaa.gov/pub/data/swdi/stormevents/csvfiles/',
#       '(Storm-Data-Export-Format.docx)',
#       'E:\stormevents\csvfiles')
     
#       '(Storm-Data-Export-Format.pdf)',
#       '(StormEvents_details-ftp_v1.0_d(\d*)_c(\d*).csv.gz)',
#       '(StormEvents_fatalities-ftp_v1.0_d(\d*)_c(\d*).csv.gz)',
#       '(StormEvents_locations-ftp_v1.0_d(\d*)_c(\d*).csv.gz)',
#BatchDownload('https://www1.ncdc.noaa.gov/pub/data/swdi/stormevents/csvfiles/legacy/',
#       '(ugc_areas.csv)',
#       'E:\stormevents\csvfiles\legacy')