处理Python中其他库导入的库中的异常的最佳实践？

Question

在Python中处理其他库导入的库中的异常的合适方法是什么？

例如，我有一个名为“ pycontrol”的库，我将其导入到主程序中。 “ pycontrol”导入“ suds”库。 反过来，“ suds”库导入“ urllib2”库。 我注意到，当“ suds”库无法连接到通过“ urllib2”访问的远程资源时，这些异常会滴加到我的主程序中。

在这一点上，我最好的猜测是将urllib2和suds导入到我的全局名称空间中，并捕获由它们抛出并且在“ pycontrol”中未处理的典型异常。

还有其他一些最佳实践来解决这一问题吗？

代码段的基本概念（无需将suds或urllib2导入全局名称空间）：

    import pycontrol.pycontrol as pc

    print "Connecting to iControl API on LTM %s..." % ltm
    try:
        b = pc.BIGIP(hostname=ltm, username=user, password=pw, 
            wsdls=wsdl_list, fromurl=True,
            debug=soap_debug)
    except (<whattocatch>), detail:
        print "Error: could not connect to iControl API on LTM %s... aborting!" % ltm
        print "Details: %s" % detail
        exitcode = 1
    else:
        print "Connection successfully established."

这是示例追溯：

Connecting to iControl API on LTM s0-bigip1-lb2.lab.zynga.com...
Traceback (most recent call last):
  File "./register.py", line 507, in <module>
    main()
  File "./register.py", line 415, in main
    b = build_bigip_object(ltm, user, pw, WSDLS, soap_debug = False)
  File "./register.py", line 85, in build_bigip_object
    debug=soap_debug)
  File "build/bdist.macosx-10.6-universal/egg/pycontrol/pycontrol.py", line 81, in __init__
  File "build/bdist.macosx-10.6-universal/egg/pycontrol/pycontrol.py", line 103, in _get_clients
  File "build/bdist.macosx-10.6-universal/egg/pycontrol/pycontrol.py", line 149, in _get_suds_client
  File "/Library/Python/2.6/site-packages/suds/client.py", line 111, in __init__
    self.wsdl = reader.open(url)
  File "/Library/Python/2.6/site-packages/suds/reader.py", line 136, in open
    d = self.fn(url, self.options)
  File "/Library/Python/2.6/site-packages/suds/wsdl.py", line 136, in __init__
    d = reader.open(url)
  File "/Library/Python/2.6/site-packages/suds/reader.py", line 73, in open
    d = self.download(url)
  File "/Library/Python/2.6/site-packages/suds/reader.py", line 88, in download
    fp = self.options.transport.open(Request(url))
  File "/Library/Python/2.6/site-packages/suds/transport/https.py", line 60, in open
    return  HttpTransport.open(self, request)
  File "/Library/Python/2.6/site-packages/suds/transport/http.py", line 62, in open
    return self.u2open(u2request)
  File "/Library/Python/2.6/site-packages/suds/transport/http.py", line 118, in u2open
    return url.open(u2request, timeout=tm)
  File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/urllib2.py", line 383, in open
    response = self._open(req, data)
  File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/urllib2.py", line 401, in _open
    '_open', req)
  File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/urllib2.py", line 361, in _call_chain
    result = func(*args)
  File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/urllib2.py", line 1138, in https_open
    return self.do_open(httplib.HTTPSConnection, req)
  File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/urllib2.py", line 1105, in do_open
    raise URLError(err)
urllib2.URLError: <urlopen error [Errno 8] nodename nor servname provided, or not known>

Answer 1

我想你回答了你自己的问题。 导入urllib2并在模块中捕获异常。

from urllib2 import URLError

try:
    # something
except URLError, e:
    # Do something in case of error.

Answer 2

为什么您需要完全捕获特定的异常？ 毕竟，从b = pc.BIGIP(...)引发的任何异常（不仅是URLError b = pc.BIGIP(...)意味着您无法继续。

我建议：

import traceback

try:
    b = pc.BIGIP(...)
except:
    traceback.print_exc()
    exitcode = 1
else:
    do_something_with_connection(b)

另一个想法：为什么要费心去捕捉异常？ Python解释器会将堆栈跟踪信息转储到stderr，并在遇到未处理的异常时退出程序：

b = bc.BIGIP(...)
do_something_with_connection(b)

或者，如果您需要写入错误日志：

import logging
import sys

def main():
   b = bc.BIGIP(...)
   do_something_with_connection(b)

if __name__ == "__main__":
    try:
        main()
    except:
        logging.exception("An unexpected error occured")
        sys.exit(1)