pythonwarningsstring-literalsquotingpython-3.12

Python 3.12 SyntaxWarning: invalid escape sequence on triple-quoted string, `\d` must be `\\d`

After updating to Python 3.12, I get warnings about invalid escape sequence on some triple-quotes comments.

Is this a new restriction? I have the habit of documenting code using triple-quoted string, but this has never been a problem prior to Python 3.12.

python3 --version
Python 3.12.0
$ ./some_script.py
/some_script.py:123: SyntaxWarning: invalid escape sequence '\d'
  """

I tried replacing all lines with \d:

20230808122708.445|INFO|C:\dist\work\trk-fullstack-test\namespaces.py

with \\d:

20230808122708.445|INFO|C:\\dist\work\trk-fullstack-test\namespaces.py

The warning disappears.

Suppressing the warning do not seem to work:

import warnings
warnings.filterwarnings('ignore', category=SyntaxWarning)

Any pointers on how to do this correctly? I hope I do not have to escape all Windows paths documented in triplequotes in our code.

Solution

  • Back in Python 3.6, using invalid escape sequences in string literals was deprecated (bpo-27364). Since then, attempting to use an invalid escape sequence has emitted a DeprecationWarning. This can often go unnoticed if you don't run Python with warnings enabled. DeprecationWarnings are silenced by default.

    Python 3.12 upgraded the DeprecationWarning to a SyntaxWarning. SyntaxWarnings are emitted by the compiler when the code is parsed, not when it's being run, so they cannot be ignored using a runtime warning filter. Unlike DeprecationWarnings, SyntaxWarnings are displayed by default, which is why you're seeing it now. This increase in visibility was intentional. In a future version of Python, using invalid escape sequences in string literals is planned to eventually become a hard SyntaxError.

    The simplest solution would be to use # comments for comments instead of string literals. Unlike string literals, comments aren't required to follow any special syntax rules. See also the discussion in Python comments: # vs. strings for more on the drawbacks of using string literals as comments.

    To address this warning in general, you can make the string literal a raw string literal r"...". Raw string literals do not process escape sequences. For example, the string "\n" contains a single newline character, whereas the string r"\n" contains the two characters \ and n.