Python - BeautifulSoup 网络爬虫

Question

我正在尝试从以下网站 (http://thedataweb.rm.census.gov/ftp/cps_ftp.html) 中抓取 URL 列表，但是按照教程我的运气为零。这是我尝试过的代码示例：

from bs4 import BeautifulSoup
import urllib2

url         = "http://thedataweb.rm.census.gov/ftp/cps_ftp.html"
page        = urllib2.urlopen(url)
soup        = BeautifulSoup(page.read())
cpsLinks    = soup.findAll(text = 
              "http://thedataweb.rm.census.gov/pub/cps/basic/")

print(cpsLinks)

我正在尝试提取这些链接：

http://thedataweb.rm.census.gov/pub/cps/basic/201501-/jan15pub.dat.gz

可能有大约 200 个这些链接。我怎样才能得到它们？

Answer 1

据我了解，您希望提取遵循特定模式的链接。 BeautifulSoup 允许您将a regular expression pattern 指定为属性值。

让我们使用以下模式：pub/cps/basic/\d+\-/\w+\.dat\.gz$'。它将匹配 pub/cps/basic/ 后跟一个或多个数字 (\d+)，后跟一个连字符 (\-)，后跟一个斜线，一个或多个字母数字字符 (\w+)，然后是 .dat.gz字符串的结尾。注意-和.在正则表达式中有特殊含义，需要用反斜杠转义。

代码：

import re
import urllib2

from bs4 import BeautifulSoup


url = "http://thedataweb.rm.census.gov/ftp/cps_ftp.html"
soup = BeautifulSoup(urllib2.urlopen(url))

links = soup.find_all(href=re.compile(r'pub/cps/basic/\d+\-/\w+\.dat\.gz$'))

for link in links:
    print link.text, link['href']

打印：

13,232,040 http://thedataweb.rm.census.gov/pub/cps/basic/201501-/jan15pub.dat.gz
13,204,510 http://thedataweb.rm.census.gov/pub/cps/basic/201401-/dec14pub.dat.gz
13,394,607 http://thedataweb.rm.census.gov/pub/cps/basic/201401-/nov14pub.dat.gz
13,409,743 http://thedataweb.rm.census.gov/pub/cps/basic/201401-/oct14pub.dat.gz
13,208,428 http://thedataweb.rm.census.gov/pub/cps/basic/201401-/sep14pub.dat.gz
...
10,866,849 http://thedataweb.rm.census.gov/pub/cps/basic/199801-/jan99pub.dat.gz
3,172,305 http://thedataweb.rm.census.gov/pub/cps/basic/200701-/disability.dat.gz