在 urllib2 中重复主机查找失败 [英] Repeated host lookups failing in urllib2

问题描述

我的代码使用 Python 的 urllib2 在多个线程中发出许多 HTTP GET 请求，将响应写入文件(每个线程一个).
在执行期间，看起来许多主机查找失败(导致名称或服务未知错误，请参阅附加的错误日志以获取示例).

I have code which issues many HTTP GET requests using Python's urllib2, in several threads, writing the responses into files (one per thread).
During execution, it looks like many of the host lookups fail (causing a name or service unknown error, see appended error log for an example).

这是由于不稳定的 DNS 服务吗?如果主机名没有改变，依赖 DNS 缓存是不好的做法吗?IE.是否应该将单个查找的结果传递到 urlopen 中?

Is this due to a flaky DNS service? Is it bad practice to rely on DNS caching, if the host name isn't changing? I.e. should a single lookup's result be passed into the urlopen?

Exception in thread Thread-16:
Traceback (most recent call last):
  File "/usr/lib/python2.6/threading.py", line 532, in __bootstrap_inner
    self.run()
  File "/home/da/local/bin/ThreadedDownloader.py", line 61, in run
     page = urllib2.urlopen(url) # get the page
  File "/usr/lib/python2.6/urllib2.py", line 126, in urlopen
    return _opener.open(url, data, timeout)
  File "/usr/lib/python2.6/urllib2.py", line 391, in open
    response = self._open(req, data)
  File "/usr/lib/python2.6/urllib2.py", line 409, in _open
    '_open', req)
  File "/usr/lib/python2.6/urllib2.py", line 369, in _call_chain
    result = func(*args)
  File "/usr/lib/python2.6/urllib2.py", line 1170, in http_open
    return self.do_open(httplib.HTTPConnection, req)
  File "/usr/lib/python2.6/urllib2.py", line 1145, in do_open
    raise URLError(err)
URLError: <urlopen error [Errno -2] Name or service not known>

更新 我的(非常简单的)代码

class AsyncGet(threading.Thread):

def __init__(self,outDir,baseUrl,item,method,numPages,numRows,semaphore):
    threading.Thread.__init__(self)
    self.outDir = outDir
    self.baseUrl = baseUrl
    self.method = method
    self.numPages = numPages
    self.numRows = numRows
    self.item = item
    self.semaphore = semaphore

def run(self):
    with self.semaphore: # 'with' is awesome.
        with open( os.path.join(self.outDir,self.item+".xml"), 'a' ) as f:
            for i in xrange(1,self.numPages+1):
                url = self.baseUrl + 
                "method=" + self.method + 
                "&item=" + self.item + 
                "&page=" + str(i) + 
                "&rows=" + str(self.numRows) + 
                "&prettyXML"
                page = urllib2.urlopen(url)
                f.write(page.read())
                page.close() # Must remember to close!

信号量是一个有界信号量，用于限制正在运行的线程总数.

The semaphore is a BoundedSemaphore to constrain the total number of running threads.

推荐答案

这不是 Python 问题，在 Linux 系统上确保 nscd (Name Service Cache Daemon) 实际上正在运行.

This is not a Python problem, on Linux systems make sure nscd (Name Service Cache Daemon) is actually running.

更新:查看您的代码，您永远不会调用 page.close() 因此泄漏套接字.

UPDATE: And looking at your code you are never calling page.close() hence leaking sockets.

这篇关于在 urllib2 中重复主机查找失败的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！