pyleri
Python Left-Right Parser
Decision gist · record as of 2026-08-14
Yes. Pyleri is actively maintained, has no dependencies, installs easily, carries no security vulnerabilities, and solves a real problem—defining grammars once and reusing them across languages. It's most valuable if you need consistent parsing logic in multiple codebases; for single-language parsing, a simpler tool may suffice.AI-flagged interpretation of the facts on this page — verify before relying
Before you install
- Low install friction with no runtime dependencies.
- The package is actively maintained, with a recent release 39 days ago and consistent commit activity.
License · maintenance · safety
permissive license (permissive) — Licensed under MIT (permissive), so you can use, modify, and distribute the package freely in commercial and private projects.
last release 2026-07-06 (39 days) · last repo commit 2026-07-06 · 124 stars
0 known vulnerabilities (OSV.dev, 2026-08-14) · 124,563 downloads/mo, #11,863 on PyPI
Alternatives
Verify before relying
from pyleri import Grammar, Keyword, Regex, Sequence
class MyGrammar(Grammar):
k_hi = Keyword('hi')
r_name = Regex('(?:"(?:[^"]*)")+')
START = Sequence(k_hi, r_name)
my_grammar = MyGrammar()
result = my_grammar.parse('hi "Iris"')
print(result.is_valid) # True- Whether the package supports Python 3.11+ despite classifiers only listing up to 3.10
- Performance characteristics when parsing large or deeply nested grammars
- Whether exported grammars in other languages maintain full feature parity with the Python version
What it is and what it does
Pyleri is a parser generator that lets you define a formal grammar as a Python class, then use it to parse and validate strings. You compose grammars from building blocks like Keywords, Regex patterns, Sequences, and Choices, then call parse() to check whether a string matches. The parser returns a result object with validation status, position, parse tree, and error expectations.
The package's main strength is cross-language export: once you define a grammar in Python, you can generate equivalent parsers in JavaScript (via jsleri), C (via libcleri), Go (via goleri), and Java (via jleri). This makes it useful for projects that need consistent parsing logic across multiple codebases—for instance, a web app with a Python backend and JavaScript frontend, or a database query language that needs to validate input in multiple services.
Use it for
- Define a query language grammar once in Python and export it to JavaScript for browser-side validation and autocompletion
- Validate domain-specific language (DSL) syntax in a Python application before processing
- Build a parser for a custom configuration file format and reuse it across Python, C, and Go microservices
- Generate error messages showing what tokens are expected at a parse failure position
- Create a grammar for a database query language and export it to multiple client libraries
Worth the install?
AI-flagged interpretation of the facts on this page. Verify before relying on it.
Yes.
Pyleri is actively maintained, has no dependencies, installs easily, carries no security vulnerabilities, and solves a real problem—defining grammars once and reusing them across languages. It's most valuable if you need consistent parsing logic in multiple codebases; for single-language parsing, a simpler tool may suffice.
Install
pyleri on PyPI
Before you install
Low install friction with no runtime dependencies. The package is actively maintained, with a recent release 39 days ago and consistent commit activity.
License in practice
Licensed under MIT (permissive), so you can use, modify, and distribute the package freely in commercial and private projects.
Quickstart
from pyleri import Grammar, Keyword, Regex, Sequence
class MyGrammar(Grammar):
k_hi = Keyword('hi')
r_name = Regex('(?:"(?:[^"]*)")+')
START = Sequence(k_hi, r_name)
my_grammar = MyGrammar()
result = my_grammar.parse('hi "Iris"')
print(result.is_valid) # TrueVerify before relying
- Whether the package supports Python 3.11+ despite classifiers only listing up to 3.10
- Performance characteristics when parsing large or deeply nested grammars
- Whether exported grammars in other languages maintain full feature parity with the Python version
Package facts
| License | permissive license permissive |
| Python support | Not specified |
| Install friction | Low. Pure-Python wheel |
| Runtime dependencies | None |
| Maintenance | Actively maintained 39 days since the last release |
| Last repo commit | |
| First released | |
| Downloads | 124,563 / month, #11,863 on PyPI 30-day window, as of 2026-08-14 |
| Known vulnerabilities | None known OSV.dev, checked 2026-08-14 |
| Classifiers | Development Status :: 5 - Production/StableIntended Audience :: DevelopersLicense :: OSI Approved :: MIT LicenseOperating System :: OS IndependentProgramming Language :: Python :: 3Programming Language :: Python :: 3 :: OnlyProgramming Language :: Python :: 3.10Programming Language :: Python :: 3.7Programming Language :: Python :: 3.8Programming Language :: Python :: 3.9Topic :: Software Development :: Libraries :: Python ModulesTopic :: Text Processing :: Linguistic |
Evidence: pyleri-1.5.1-py3-none-any.whl
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