无法在python中捕获异常

Question

我使用salt，当我运行exec_state('update_salt')时，会引发以下异常（下面的代码）：

  File "/usr/lib/python2.6/site-packages/salt/client/__init__.py", line 1582, in __init__
    caller = salt.client.Caller()
  File "/usr/lib/python2.6/site-packages/salt/minion.py", line 283, in __init__
    for key, val in data.items():
  File "/usr/lib/python2.6/site-packages/salt/minion.py", line 300, in gen_modules

  File "/usr/lib/python2.6/site-packages/salt/loader.py", line 286, in render
    opts,
salt.exceptions.LoaderError: The renderer yaml_jinja is unavailable, this error is often because the needed software is unavailable

我尝试通过try和catch块来处理它：

try:
   result = exec_state('update_salt')
   if not result:
       return False
except:
   print "got it.."
   result = exec_state('update_salt_light')
   if not result:
       return False

但它在第一次尝试时仍然失败，并且没有到达异常块（没有打印）。为什么呢？