linux-kernel - Re: [PATCH] selftests/tpm2: Change exception handling to be Python 3 compatible

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Date:   Tue, 14 Apr 2020 10:38:06 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Ezra Buehler <ezra@...yb.ch>
Cc:     Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org,
        linux-integrity@...r.kernel.org,
        Tadeusz Struk <tadeusz.struk@...el.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] selftests/tpm2: Change exception handling to be Python 3
 compatible

On Tue, Apr 14, 2020 at 07:45:33AM +0200, Ezra Buehler wrote:
> Hi Jarkko,
> 
> On 13 Apr 2020, at 20:04, Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com> wrote:
> > 
> > On Mon, Apr 13, 2020 at 07:02:20AM +0200, Ezra Buehler wrote:
> >> Hi Jarkko,
> >> 
> >> On 12 Apr 2020, at 19:07, Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com> wrote:
> >>> 
> >>> On Sun, Apr 12, 2020 at 05:02:27PM +0200, Ezra Buehler wrote:
> >>>> Hi Jarkkon,
> >>>> 
> >>>>> On 12 Apr 2020, at 16:36, Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com> wrote:
> >>>>> +        except ProtocolError(e):
> >>>> 
> >>>> Should this not be
> >>>> 
> >>>>       except ProtocolError as e:
> >>> 
> >>> Unless there is a functional difference, does it matter?
> >>> 
> >>> /Jarkko
> >> 
> >> Well, your patch confuses me a lot. It looks to me like you are passing
> >> the undefined `e` variable to the constructor.
> >> 
> >> When I run flake8 on it I get following error (among others):
> >> 
> >>    F821 undefined name 'e'
> > 
> > I don't know what flake8 is.
> 
> https://flake8.pycqa.org/en/latest/
> 
> >> What I suggested is the standard syntax:
> >> https://docs.python.org/3/tutorial/errors.html
> > 
> > It passed the Python 3 interpreter.
> 
> That is because it is technically valid syntax.
> 
> >> Did you test this? You should get an error as soon as an exception
> >> occurs.
> > 
> > Yes. Interpreter did not complain. I did not know that the language
> > is broken that way that you have to exercise the code path to get
> > a syntax error.
> 
> That is due to the dynamic nature of Python. You won’t get a syntax
> error. You will get an exception:
> 
>     NameError: name 'e' is not defined
> 
> Python has to assume that `e` might be defined at runtime. However,
> style checkers will complain.

OK, I'm aware about the dynamic nature but in this case it is somewhat
counter intuitive since it is part of the exception clause. You'd except
the Python interpreter to complain.

So, is Flake8 like the standard to be used?

/Jarkko