[Python-ideas] Make undefined escape sequences have SyntaxWarnings

[Mike Graham]

On Wed, Oct 10, 2012 at 8:08 PM, Steven D'Aprano <steve at pearwood.info> wrote:
> On 11/10/12 07:08, Mike Graham wrote:
>>
>> On Wed, Oct 10, 2012 at 3:46 PM, Antoine Pitrou<solipsis at pitrou.net>
>> wrote:
>>>
>>> On Wed, 10 Oct 2012 15:36:08 -0400
>>> Mike Graham<mikegraham at gmail.com>  wrote:
>
>
>>>> The literal"\c" should be an error
>
>
> Who says so? My bash shell disagrees with you:

Frankly, I don't look to bash for sensible language design advice. I
think concepts like "In the face of ambiguity, refuse the temptation
to guess" guides how we should see the decision here. "Backslash is
for escape sequences except when it's not" seemed like an
obviously-misfortunate thing to me. I'm truly perplexed people see it
as a feature they're eager to use, but I guess I should learn
something from that.

>> Regular expressions are difficult if you're remembering which escape
>> sequences exist and are easy if you're using raw string literals.
>
> Just because some people find it hard to remember doesn't mean that it
> should be an error *not* to use raw strings.

I didn't say that it should be an error not to use raw strings. I was
saying that the implication that this suggestion makes constructing
regex strings hard is silly and mentioning the thing that makes them
easy. I'm not suggesting that you shouldn't be able to use normal
string literals.

Antoine went on to point out that things like "\t" worked in regex
strings. This is an unrelated feature that I never suggested altering.
In that case, a tab character in your string is regarded like \t. This
behavior would remain.

I think four string escapes have been added since versions of Python I
was aware of. Writing code like "ab\c" seems seedy in light of that

Mike