With Python 3.12, the following change was made:

A backslash-character pair that is not a valid escape sequence now generates a SyntaxWarning, instead of DeprecationWarning. For example, re.compile("\d+.\d+") now emits a SyntaxWarning ("\d" is an invalid escape sequence, use raw strings for regular expression: re.compile(r"\d+.\d+")). In a future Python version, SyntaxError will eventually be raised, instead of SyntaxWarning. (Contributed by Victor Stinner in gh-98401.)

This causes warnings, which will become errors in future versions, such as

chap02/calc/calc_lexer.py:43: SyntaxWarning: invalid escape sequence '\e'
tokens.append(Token('EOF', '\eof'))

Replacing '\eof' with r'\eof' is sufficient to resolve this.

I diff'ed the output of python3.11 running the upstream code vs python 3.12 running the modified code using these commands:

diff <(python3.11 upstream/chap02/calc/calc_lexer.py) <(python3.12 plipy-code/chap02/calc/calc_lexer.py)

There were no differences between the two.