On 26Nov2018 09:03, Steven D'Aprano <st...@pearwood.info> wrote:
On Sun, Nov 25, 2018 at 10:43:10PM +0530, srinivasan wrote:
1. Am trying to improve the below code with "try" and "exception",
could
you please help me how "try" and "exception" can be used on the below code
snippet. I hope in my code with try and exception, seems to be a bug.
As a beginner, you should normally not use try...except to report
errors. You should learn how to diagnose errors by reading the
traceback. Covering up the traceback with try...except makes debugging
harder.
Very true, but...
Your use here:
* try:*
* cmd = "nmcli device wifi connect '%s' password '%s'" % (ssid, pw)*
* proc = subprocess.Popen(cmd, stdout=subprocess.PIPE,
stderr=subprocess.PIPE, shell=True, universal_newlines=True)*
* stdout, stderr = proc.communicate()*
* retcode = proc.returncode*
* print("printing stdout!!!!!!!!!!", stdout)*
* print("printing retcode!!!!!!!!!!", retcode)*
* except subprocess.CalledProcessError as e:*
* s = """While executing '{}' something went wrong.*
* Return code == '{}'*
* Return output:\n'{}'*
* """.format(cmd, e.returncode, e.output,
shell=enable_shell)*
* raise AssertionError(s)*
[...]
But even if it doesn't fail, the next line:
raise AssertionError(s)
is an abuse of exceptions. The failure here is *not* an assertion, and
you shouldn't use AssertionError. You wouldn't use TypeError or
UnicodeEncodeError or AttributeError. "AssertionError" should not be
used for "some arbitrary error". [...]
My opinion is, you should remove that try...except altogether. I don't
think that it helps your code, even if it worked. Calls to Popen can
fail in many, many ways, and it seems pointless to single out just one
of them and to replace the useful traceback and error message with a
less accurate one.
I'd add one qualificaion here: it may be that he wants to report this
exception in particular, while still not "handling it". In which case
I'd advocate something like:
try:
... Popen stuff ...
except subprocess.CalledProcessError as e:
s = ....
print(s, file=sys.stderr)
raise
i.e. report some special message, then _reraise_ the original exception.
In this way he gets to keep the original exception and traceback for
debugging, which still making whatever special message he wanted to
make.
Cheers,
Cameron Simpson <c...@cskk.id.au>
_______________________________________________
Tutor maillist - Tutor@python.org
To unsubscribe or change subscription options:
https://mail.python.org/mailman/listinfo/tutor
