[Python-Dev] Emit SyntaxWarning on unrecognized backslash escapes?

[Thomas Wouters]

On Tue, Feb 24, 2015 at 5:37 PM, Ethan Furman <ethan at stoneleaf.us> wrote:

> On 02/24/2015 02:58 AM, Chris Angelico wrote:
> > On Tue, Feb 24, 2015 at 7:40 PM, M.-A. Lemburg <mal at egenix.com> wrote:
> >> I think the easiest way would be to tweak the error message
> >> output to indicate the real problem.
> >>
> >> At the moment, you get:
> >>
> >>>>> open('c:\test.txt')
> >> Traceback (most recent call last):
> >>   File "<stdin>", line 1, in <module>
> >> FileNotFoundError: [Errno 2] No such file or directory: 'c:\test.txt'
> >>
> >> which isn't helpful.
> >
> > The problem isn't the cases where the file can't be found. Those can
> > be dealt with fairly easily, one way or another. The problem is much,
> > much earlier, when the student was using "c:\sample.txt" and
> > everything was working fine. Then he changed the code over to use his
> > own file instead of the provided sample, and at the same time,
> > switched from using open() to using csv.reader(open()), and moved all
> > the code into a function, and fixed three other bugs, and now it isn't
> > working. And he can't figure out why.
> >
> > That's why I'd like "c:\sample.txt" to raise a warning.
> >
> > Should I start writing up a PEP? Is that the way forward with this?
>
> Go for it.
>
> I think the solution will be two pieces:
>
>   - deprecating unknown backslash-escapes, with the goal of eventually
> being a SyntaxError
>     (this removes a wart from the language, as well as allowing a warning
> backport to 2.7)
>
>   - M.A.Lemburg's idea of changing the exception message in key places to
> make a successful
>     backslash replace obvious
>     (FileNotFoundError: [Errno 2] No such file or directory:
> 'c:[\t]est.txt' - warning: embedded escapes)
>

Any ideas on how this check could be implemented? How would it distinguish
\t from an actual tab in the string literal, or "C:\x64-python" from
"C:\d-python"...?


>
> --
> ~Ethan~
>
>
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-- 
Thomas Wouters <thomas at python.org>

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