Unexpected behaviour with DeprecationWarning, Python 3.7 and escape codes

[D'Arcy Cain]

On 2018-08-23 06:08 AM, Peter via Python-list wrote:
> I understand that Python 3.7 now issues DeprecationWarning for code
> entered in the interactive shell and also for single-module programs. I
> see this behaviour with:
> 
> C:\wrk> python
> python 3.7.0 (v3.7.0:...
>>>> import imp
> __main__:1: DeprecationWarning: the imp module is deprecated...

Valid warning.

> But if I use an unknown escape code, then the expected warning doesn't
> issue:
> 
>>>> print('Hello \world')
> Hello \world
> 
> But if I explicitly turn on default warnings, then I do get it:
> 
> C:\wrk> python -Wd
>>>> print('Hello \world')
> <stdin>:1: DeprecationWarning: invalid escape sequence \w
> Hello \world

I don't know why it issues DeprecationWarning but this is not the same
as the previous line.  In this case \w is invalid and, as far as I know,
 has always been invalid.  I think it should be a different warning but
I do understand why it is in a different code path in Python.

It doesn't issue any warning in 2.7 by the way.  It still prints the
same thing so it is still an invalid escape sequence.

-- 
D'Arcy J.M. Cain
Vybe Networks Inc.
http://www.VybeNetworks.com/
IM:darcy at Vex.Net VoIP: sip:darcy at VybeNetworks.com