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

[Thomas Wouters]

On Tue, Feb 24, 2015 at 1:00 PM, Joao S. O. Bueno <jsbueno at python.org.br>
wrote:

> On 23 February 2015 at 18:39, Greg Ewing <greg.ewing at canterbury.ac.nz>
> wrote:
> > Serhiy Storchaka wrote:
> >>
> >> The problem is that the user don't know that he should read the
> >> documentation. It just find that his script works with "C:\sample.txt",
> but
> >> doesn't work with "D:\test.txt". He has no ideas what happen.
> >
> >
> > Even with the syntax error, there are filenames that
> > will mysteriously fail, e.g. "C:\ninjamoves.txt".
>
>
> That is the reason I urge folks to think about the root cause,
> and check if this proposal is the best way to tackle it:

The failing cases are the ones that won't be affected by this change at all
> -
> as they are valid escaped strings!
>

I would argue that some cases working is the root cause of the confusion.
If *none* of the cases work, it would be a lot less confusing, even if the
error message is different. Trying to make the error messages more similar,
or more identifying, may be a good idea (as long as they aren't misleading
when people *meant* to use escape sequences in a string) but fortunately
that's separate from making the cases that current silently and
misleadingly work, emit a warning (or error.)

Emitting a warning does not address the question 'why does "C:\test" not
exist when I see it in Explorer.' It does address the question 'why does my
program break when I change "C:\Test" to "C:\test". It also addresses 'why
does my regexp not work when I change "\d+" to "\b\d+", and unlike changing
the error message for opening files it is much closer, in time and space,
to the actual problem. It's a helpful thing regardless of what other
changes are made.

I do expect there to need to be a much longer deprecation period than one
or even two releases, though: there is a lot of code that uses the
misfeature, mostly by accident (not realizing they should be using r'',
etc.)



> There will be no error for
> c:\tmp\myfile.txt - it will ever be just "file not found" - unless the
> warning comes to
> using "\" as file path separator (and no, I don  think just doing that
> would properly
> address the issue as well).
>
> Could we just use Guido's time machine and go back to the point in time
> where
> some MS head decided to go with "\" instead of "/", and deliver a well
> placed punch? :-)
>
> Or maybe have IOError for "file not found" to get some fuzzy logic and
> display a more verbose error message if there are "\n"s and "\t"s on
> the filename
> and platform is Windows?  I think that  could go along the proposal for
> deprecating non-escaping "\<x>" sequences .
>
> By the way,  although I am writing to get the root issue covered, I think
> deprecating them would be a good thing, yes. Despite my previous comment
> on deprecating code that works, on a deeper though it _is_ worth the issue.
>
>   js
>  -><-
>
>
>
> >
> > --
> > Greg
> >
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> >
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-- 
Thomas Wouters <thomas at python.org>

Hi! I'm an email virus! Think twice before sending your email to help me
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