Previous attempt in 2018:

• Commit:6543912
• Serhiy only changed the Python parser, not codecs:rationale
• The new SyntaxWarning was seen in multiple projects: docutils (fixed), bottle, SymPy (bug in a docstring)
• SyntaxWarning are only emitted once, and only when a Python file is parsed: when a cached PYC file is used, not warning is emitted
• Serhiy reverted his change

I tested the Python test suite with SyntaxWarning treated as error: it does pass.

$ PYTHONWARNINGS=error::SyntaxWarning ./python -W error::SyntaxWarning -m test -j0 -r -u all,-gui

This issue mostly hit code defining regular expressions. Example in BeautifulSoup 3.2.2:

$ pycodestyle --select W605 $(find -name "*.py")./BeautifulSoup.py:455:52: W605 invalid escape sequence '\d'./BeautifulSoup.py:455:73: W605 invalid escape sequence '\w'./BeautifulSoup.py:574:47: W605 invalid escape sequence '\d'./BeautifulSoup.py:574:66: W605 invalid escape sequence '\w'./BeautifulSoup.py:1080:38: W605 invalid escape sequence '\s'./BeautifulSoup.py:1589:36: W605 invalid escape sequence '\s'./BeautifulSoup.py:1933:16: W605 invalid escape sequence '\?'./BeautifulSoup.py:1933:46: W605 invalid escape sequence '\?'./BeautifulSoup.py:1935:35: W605 invalid escape sequence '\s'

Examples of code, re.compile() calls:

    BARE_AMPERSAND_OR_BRACKET = re.compile("([<>]|"                                           + "&(?!#\d+;|#x[0-9a-fA-F]+;|\w+;)"                                           + ")")(...)                      (re.compile('<!\s+([^<>]*)>'),(...)        xml_encoding_match = re.compile(            '^<\?.*encoding=[\'"](.*?)[\'"].*\?>').match(xml_data)

I tested the Python test suite with SyntaxWarning treated as error: it does pass.

Did you remove all pyc files and regenerate frozen modules before tests? Also try to regenerate generated code using the new Python binary as PYTHON_FOR_REGEN.

Did you remove all pyc files and regenerate frozen modules before tests? Also try to regenerate generated code using the new Python binary as PYTHON_FOR_REGEN.

I ranPYTHONWARNINGS=error::SyntaxWarning make regen-all PYTHON_FOR_REGEN=./python: it works as expected.

@serhiy-storchaka:

Perhaps SyntaxWarning could be raised for invalid octals too. It is a more obvious error, and less common, so it may have lesser deprecation period.

Ok, I updated my PR: Use SyntaxWarning for invalid octal sequence.

Hum, I messed up my PR so I squashed two commits and I fixed my PR:

• invalid octal sequence and invalid escape sequence now both emit SyntaxWarning (and will emit SyntaxError in the future)
• codecs.escape_decode() and codecs.unicode_escape_decode() are left unchanged

I also mentioned the future convertion to SyntaxError in the doc (What's New / NEWS entries).

@mdickinson@serhiy-storchaka@hugovk: Would you mind to review my PR?

Did you remove all pyc files?

find -name'*.py[co]' -exec rm -rf'{}' +

Let me try these commands:

export PYTHONWARNINGS=error::SyntaxWarning git clean -fdx./configure --with-pydebug CFLAGS=-O0makemake regen-all PYTHON_FOR_REGEN=./pythonmake./python -c 's = "\477"'

The last command failsas expected with:

  File "<string>", line 1    s = "\477"        ^^^^^^SyntaxError: invalid octal escape sequence '\477'

Oops, test_string_literals didn't work when run with./python -W error::SyntaxWarning: it's now fixed.

I ran the test suite with:

export PYTHONWARNINGS=error::SyntaxWarning ./python -W error::SyntaxWarning -m test -j0 -r -u all,-gui

Note: I would prefer to run the whole test suite with-Werror, but it fails even without this PR :-( Python currently emits many deprecation warnings for example :-(