如何将"catch-all“异常子句应用于复杂的python web抓取脚本？

Question

我有一个CSV格式的100个网站的列表。所有的站点都有相同的通用格式，包括一个包含7列的大表。我写了这个脚本，从每个网站的第7列提取数据，然后将这些数据写入文件。然而，下面的脚本部分工作:打开输出文件(在运行脚本之后)显示跳过了一些东西，因为它只显示了98次写入(显然，该脚本还注册了许多异常)。关于如何在此上下文中实现“捕获异常”的指导将不胜感激。谢谢!

import csv, urllib2, re
def replace(variab): return variab.replace(",", " ")

urls = csv.reader(open('input100.txt', 'rb'))  #access list of 100 URLs
for url in urls:
    html = urllib2.urlopen(url[0]).read()  #get HTML starting with the first URL
    col7 = re.findall('td7.*?td', html)  #use regex to get data from column 7
    string = str(col7)  #stringify data
    neat = re.findall('div3.*?div', string)  #use regex to get target text  
    result = map(replace, neat)  #apply function to remove','s from elements
    string2 = ", ".join(result)  #separate list elements with ', ' for export to csv
    output = open('output.csv', 'ab') #open file for writing 
    output.write(string2 + '\n') #append output to file and create new line
    output.close()

返回：

Traceback (most recent call last):
 File "C:\Python26\supertest3.py", line 6, in <module>
  html = urllib2.urlopen(url[0]).read()
 File "C:\Python26\lib\urllib2.py", line 124, in urlopen
  return _opener.open(url, data, timeout)
 File "C:\Python26\lib\urllib2.py", line 383, in open
  response = self._open(req, data)
 File "C:\Python26\lib\urllib2.py", line 401, in _open
  '_open', req)
 File "C:\Python26\lib\urllib2.py", line 361, in _call_chain
  result = func(*args)
 File "C:\Python26\lib\urllib2.py", line 1130, in http_open
  return self.do_open(httplib.HTTPConnection, req)
 File "C:\Python26\lib\urllib2.py", line 1103, in do_open
  r = h.getresponse()
 File "C:\Python26\lib\httplib.py", line 950, in getresponse
  response.begin()
 File "C:\Python26\lib\httplib.py", line 390, in begin
  version, status, reason = self._read_status()
 File "C:\Python26\lib\httplib.py", line 354, in _read_status
  raise BadStatusLine(line)
BadStatusLine
>>>>

Answer 1

将for循环的主体放入：

for url in urls:
  try:
    ...the body you have now...
  except Exception, e:
    print>>sys.stderr, "Url %r not processed: error (%s) % (url, e)

(或者，使用logging.error而不是愚蠢的print>>，如果您已经在使用标准库的logging模块，并且应该使用；-))。

Answer 2

我建议您阅读Python文档，特别是第8.3节--处理异常。