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

[Ethan Furman]

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)

--
~Ethan~

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