Python调试不如强类型的语言方便，显示调用栈有时非常必要，inspect模块很好用
import inspect inspect.stack()
inspect.stack()返回的是一个函数栈帧列表如（已经做了一个for e in inspect(): print e 转化）
(<frame object at 0x7f6ec27b2050>, '/usr/lib/python2.7/dist-packages/oslo/config/cfg.py', 495, '_is_opt_registered', [' st = inspect.stack()\n'], 0)
(<frame object at 0x7f6ec2807d00>, '/usr/lib/python2.7/dist-packages/oslo/config/cfg.py', 1163, '_register_opt', [' if _is_opt_registered(self._opts, opt):\n'], 0)
(<frame object at 0x7f6ec280bb90>, '/usr/lib/python2.7/dist-packages/oslo/config/cfg.py', 1710, 'register_opt', [' return group._register_opt(opt, cli)\n'], 0)
(<frame object at 0x1a4f180>, '/usr/lib/python2.7/dist-packages/oslo/config/cfg.py', 1591, '__inner', [' return f(self, *args, **kwargs)\n'], 0)
(<frame object at 0x1a805f0>, '/usr/lib/python2.7/dist-packages/oslo/config/cfg.py', 1723, 'register_opts', [' self.register_opt(opt, group, clear_cache=False)\n'], 0)
(<frame object at 0x1a941f0>, '/usr/lib/python2.7/dist-packages/oslo/config/cfg.py', 1587, '__inner', [' result = f(self, *args, **kwargs)\n'], 0)
(<frame object at 0x1ac0bb0>, '/usr/lib/python2.7/dist-packages/nova/openstack/common/db/options.py', 131, '<module>', ["CONF.register_opts(database_opts, 'database')\n"], 0)
(<frame object at 0x7f6ec2870aa0>, '/usr/lib/python2.7/dist-packages/nova/config.py', 21, '<module>', ['from nova.openstack.common.db import options\n'], 0)
(<frame object at 0x7f6ec381c050>, '/usr/lib/python2.7/dist-packages/nova/cmd/api.py', 27, '<module>', ['from nova import config\n'], 0)
(<frame object at 0x7f6ec4f4cc20>, '/usr/bin/nova-api', 6, '<module>', ['from nova.cmd.api import main\n'], 0)