neologism

A dynamically modifiable context-free grammar library for Python.

neologism loads bison-style yacc files directly, exposes the grammar as a DCFG object you can mutate (add or remove rules, promote nonterminals to terminals, substitute symbols, and so on), and enumerates the sentences the resulting grammar produces.

The mutation-after-load workflow is the distinguishing feature: most grammar libraries either parse using a grammar, or model a CFG as data, but not both with a path from a real .y file to programmatic manipulation.

Install

pip install neologism

bison must be available on PATH to load .y files. It is invoked at runtime to convert the yacc file to the XML form neologism consumes.

A taste

from neologism import DCFG, Rule

dcfg = DCFG.from_yacc_file("my-grammar.y")

# Treat LL_NUMBER as a terminal and substitute a pretty placeholder
dcfg.make_symbol_terminal("LL_NUMBER")
dcfg.add_rule(Rule("LL_NUMBER", ("<number>",)))

# Stream every sentence the transformed grammar produces
for sentence in dcfg.iter_sentences():
    print(" ".join(sentence))

A walkthrough of this pipeline lives in Quickstart.

Real-world consumer

axosyslog-cfg-helper walks the AxoSyslog bison grammar, applies module-specific transformations, and enumerates every driver invocation to build a configuration-option database. It exercises every part of the API and is the load-bearing consumer driving neologism’s roadmap.

Contents

• Quickstart
  • A first DCFG from scratch
  • Terminals vs nonterminals
  • Loading a real yacc file
  • Transforming a loaded grammar
  • Enumerating sentences
  • A bigger consumer
• API reference
  • DCFG
  • Rule
  • YaccDecodeError

Project links

• Source on GitHub

• Changelog

• Issue tracker

• PyPI

License

GPL-3.0-or-later.