common mistakes in this simple program

Ganesh Pal ganesh1pal at
Mon Feb 29 13:21:37 EST 2016

>> How do we reraise the exception in python ,  I have used raise not
>> sure how to reraise the exception
> raise with no arguments will reraise the exception currently being handled.
> except Exception:
>     logging.error("something went wrong")
>     raise

Thanks Ian for taking time and looking into the code ,  o k raise
keyword for raising exception is fine .

>>>>         assert ret ==0,"ERROR (ret %d): " \
>>>>                 " \nout: %s\nerr: %s\n" % (ret, out, err)
>>>>     except Exception as e:
>>>>         print("Failed to run %s got %s" % (cmd, e))
>>>>         return False
>>>>     return True
>>>> def prep_host():
>>>>     """
>>>>     Prepare clustering
>>>>     """
>>>>     for cmd in ["ls -al",
>>>>                 "touch /tmp/file1",
>>>>                 "mkdir /tmp/dir1"]:
>>>>         try:
>>>>             if not run_cmd_and_verify(cmd, timeout=3600):
>>>>                 return False
>>>>         except:
>>> What exceptions are you expecting this to catch? run_cmd_and_verify
>>> already catches any expected exceptions that it raises.

In my case the exception is nothing but the error  example if  we plan
to run the command  say  #ifconfig -a and the command fails because of
a type ( say u ran #igconfig -a).

we will the output as

# Failed to run igconfig -a got Error (ret=127)
out :
error: command not found: igconfig

So the execption is the error i.e Error (ret=127) out : error: command
not found: igconfig,  Iam fine with this behaviour.

> But that exception is already caught by the run_cmd_and_verify
> function, so what exception are you expecting to be caught *here*?

I wanted to run the command in a loop  and have a fxn for the pattern
that repeats in this case the function is run_cmd_and_verify  , the
only known way to me was using try with expect

I thought I will use try and have pass in except which  you don't recommend

   for cmd in ["ls -al",
                 "touch /tmp/file1",
                "mkdir /tmp/dir1"]:
                   if not run_cmd_and_verify(cmd, timeout=3600):
                        print "running command failed "
                   return False

> You should virtually never just pass in an exception handler. Either
> handle the exception, or log it and reraise it. If you're going to do
> neither of those things, then don't use a try-except at all.

What alternative do I have other than try-expect ? can try - else be
used  for my case?


More information about the Python-list mailing list