rply
A pure Python Lex/Yacc that works with RPython
Decision gist · record as of 2026-08-14
Yes, if you need a parser generator and are comfortable with abandoned software. RPLY is stable, has no known vulnerabilities, and works well for building parsers in pure Python. However, it has received no updates since January 2021 and is no longer maintained—use it only for projects where you can tolerate no future fixes or Python version support updates. For active alternatives, consider PLY or more modern parser libraries.AI-flagged interpretation of the facts on this page — verify before relying
Before you install
- Requires understanding of lexer/parser concepts; RPython support is optional but the box pattern (wrapping values) is necessary for RPython compatibility.
- Installation is straightforward with a single lightweight dependency (appdirs) and a pure-Python wheel.
- However, the package is abandoned—last released in January 2021 with no activity since, so expect no bug fixes or maintenance.
License · maintenance · safety
BSD 3-Clause License (permissive) — BSD 3-Clause License is permissive, allowing commercial and private use with minimal restrictions; attribution and license inclusion are required.
last release 2021-01-27 (2025 days)
0 known vulnerabilities (OSV.dev, 2026-08-14) · 542,262 downloads/mo, #6,089 on PyPI
Alternatives
Verify before relying
pip install rply
from rply import LexerGenerator, ParserGenerator
from rply.token import BaseBox
lg = LexerGenerator()
lg.add("NUMBER", r"\d+")
lg.add("PLUS", r"\+")
lg.ignore(r"\s+")
pg = ParserGenerator(["NUMBER", "PLUS"])
@pg.production("expr : NUMBER PLUS NUMBER")
def expr(p):
return int(p[0].getstr()) + int(p[2].getstr())
lexer = lg.build()
parser = pg.build()
result = parser.parse(lexer.lex("1 + 2"))- Whether the package still works reliably with Python 3.8+ given the 2021 release date and no recent maintenance.
- Whether cached parsers (cache_id feature) remain compatible across Python versions without manual invalidation.
What it is and what it does
RPLY is a parser generator library that lets you define lexical and syntactic rules for parsing custom languages or domain-specific syntax. You write token rules (lexer) and grammar productions (parser) as Python decorators, then build a lexer and parser that can tokenize and parse input strings. It's a direct port of PLY (Python Lex-Yacc) with a cleaner API and support for RPython, a statically-typed Python subset used by PyPy.
The library is designed for building interpreters, domain-specific languages, or any tool that needs to parse structured text. It handles operator precedence, error reporting with source positions, and optional caching of compiled grammars. The box pattern (wrapping values in classes) is built in for RPython compatibility but can be ignored in pure-Python projects.
Use it for
- Build a simple calculator or expression evaluator that parses and computes mathematical expressions.
- Create a domain-specific language (DSL) parser for configuration files or query languages.
- Implement an interpreter for a toy programming language or scripting syntax.
- Parse structured text formats where regex alone is insufficient.
- Develop a PyPy-compatible parser when RPython support is required.
Worth the install?
AI-flagged interpretation of the facts on this page. Verify before relying on it.
Yes, if you need a parser generator and are comfortable with abandoned software.
RPLY is stable, has no known vulnerabilities, and works well for building parsers in pure Python. However, it has received no updates since January 2021 and is no longer maintained—use it only for projects where you can tolerate no future fixes or Python version support updates. For active alternatives, consider PLY or more modern parser libraries.
Install
rply on PyPI
Before you install
Installation is straightforward with a single lightweight dependency (appdirs) and a pure-Python wheel. However, the package is abandoned—last released in January 2021 with no activity since, so expect no bug fixes or maintenance.
Requires understanding of lexer/parser concepts; RPython support is optional but the box pattern (wrapping values) is necessary for RPython compatibility.
License in practice
BSD 3-Clause License is permissive, allowing commercial and private use with minimal restrictions; attribution and license inclusion are required.
Quickstart
pip install rply
from rply import LexerGenerator, ParserGenerator
from rply.token import BaseBox
lg = LexerGenerator()
lg.add("NUMBER", r"\d+")
lg.add("PLUS", r"\+")
lg.ignore(r"\s+")
pg = ParserGenerator(["NUMBER", "PLUS"])
@pg.production("expr : NUMBER PLUS NUMBER")
def expr(p):
return int(p[0].getstr()) + int(p[2].getstr())
lexer = lg.build()
parser = pg.build()
result = parser.parse(lexer.lex("1 + 2"))Verify before relying
- Whether the package still works reliably with Python 3.8+ given the 2021 release date and no recent maintenance.
- Whether cached parsers (cache_id feature) remain compatible across Python versions without manual invalidation.
Package facts
| License | BSD 3-Clause License permissive |
| Python support | Not specified |
| Install friction | Low. Pure-Python wheel |
| Runtime dependencies | 1 packageappdirs |
| Maintenance | Abandoned 2,025 days since the last release |
| First released | |
| Downloads | 542,262 / month, #6,089 on PyPI 30-day window, as of 2026-08-14 |
| Known vulnerabilities | None known OSV.dev, checked 2026-08-14 |
Evidence: rply-0.7.8-py2.py3-none-any.whl
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See also ply · sly · phply · pygmars · Parsley · pyparsing · funcparserlib · flexparser · lark-parser · PyMeta3