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Version 1.0! Big release with breaking changes

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@erezsh erezsh released this 15 Nov 08:22
· 313 commits to master since this release

Over the last few years, Lark has grown to become a comprehensive toolkit for parsing structured text.

Today, I'm happy to announce the long anticipated version 1.0 of Lark, marking the API as stable.

We've made quite a few breaking changes, in order to achieve congruous API with as little "gotchas" as possible. Upgrading to version 1.0 might require a few changes to your project.

Breaking changes

  • Dropped Python 2 support! Lark now only supports Python 3.6 and up.

  • Install lark using pip install lark (instead of lark-parser ).

  • maybe_placeholders is now True by default.

  • Renamed TraditionalLexer to BasicLexer, and 'standard' lexer option to 'basic'.

  • Default priority is now 0, for both terminals and rules (used to be 1 for terminals).

  • Discard mechanism is now done by returning Discard, instead of raising it as an exception.

  • use_accepts in UnexpectedInput.match_examples() is now True by default.

  • v_args(meta=True) now gives meta as the first argument. i.e. (meta, children).


  • Better type annotations
  • Support for terminal priorities for dynamic Earley
  • Python3 grammar is now officially supported, and can be used via %import python (...)
  • New experimental feature: Tree Templates
  • Various bugfixes


Many thanks to all our contributors and donors, who made this release possible. Special thanks goes to -

  • @MegaIng, for innumerous features, bugfixes, and code-reviews.
  • @chanicpanic, for his immense and continual contributions to the Earley parser, and for helping with the v1.0 effort.
  • @erezsh, for being myself.