Re: Correct syntax for pathological re.search()

On 2024-10-08 21:59, Alan Bawden via Python-list wrote:

Karsten Hilbert <Karsten.Hilbert@gmx.net> writes:
             Python 3.11.2 (main, Aug 26 2024, 07:20:54) [GCC 12.2.0] on linux
            Type "help", "copyright", "credits" or "license" for more information.
            >>> tex = '\sout{'
            >>> tex
            '\sout{'
            >>>
     Am I missing something ?
 You're missing the warning it generates:
          > python -E -Wonce
         Python 3.11.2 (main, Aug 26 2024, 07:20:54) [GCC 12.2.0] on linux
         Type "help", "copyright", "credits" or "license" for more information.
         >>> tex = '\sout{'
         <stdin>:1: DeprecationWarning: invalid escape sequence '\s'
         >>>

You got lucky that \s in invalid. If it had been \t you would've got a tab character.
Historically, Python treated invalid escape sequences as literals, but it's deprecated now and will become an outright error in the future (probably) because it often hides a mistake, such as the aforementioned \t being treated as a tab character when the user expected it to be a literal backslash followed by letter t. (This can occur within Windows file paths written in plain string literals.)