lark-parser/lark

Add support for the `a` and `L` regex flags

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#1,527 opened on Apr 21, 2025

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 (5 comments) (0 reactions) (0 assignees)Python (4,275 stars) (384 forks)batch import
enhancementgood first issue

Description

Lark currently only supports the flags imslux, however Python supports two additional ones, which perhaps some people will find useful.

While users can still use inline flags, it might be nice for Lark to support it as part of the syntax, and it should be pretty easy.

https://docs.python.org/3/library/re.html#flags

Contributor guide

Tech stack
python
Domain
backendtooling
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Understanding of Python regex flagsFamiliarity with Lark's lexer implementation
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70
Research direction
The issue is to add support for `a` (ASCII) and `L` (locale) flags in Lark's regex syntax. Currently Lark supports flags `imslux`. The implementation likely involves modifying the lexer or grammar to recognize these new flags. Look at how existing flags are parsed and applied, potentially in files like `lark/lexer.py` or `lark/grammar.py`. The maintainers have not yet responded, so no specific guidance is available. A good starting point is to examine the current flag handling code and add the two new flags in a similar manner.