package pyre-ast

  1. Overview
  2. Docs
Full-fidelity Python parser in OCaml


Dune Dependency






pyre-ast is an OCaml library to parse Python source files into abstract syntax trees. Under the hood, it relies on the CPython parser to do the parsing work and therefore the result is always 100% compatible with the official CPython implementation.

Published: 04 Nov 2022



pyre-ast is an OCaml library to parse Python files.

The library features its full-fidelity to the official Python spec. Apart from a few technical edge cases, as long as a given file can be parsed by the CPython interpreter, pyre-ast will be able to parse the file without any problem. Furthermore, abstract syntax trees obtained from pyre-ast is guaranteed to 100% match the results obtained by Python's own ast.parse API, down to every AST node and every line and column number.

Another notable feature of this library is that it represents the Python syntax using the tagless-final style. This style typically offers more flexibility and extensibility for the downstream consumers of the syntax, and allow them to build up their analysis without explicitly constructing a syntax tree. On the other hand, this library does offer a tranditional "concrete" syntax tree structure as well, for developers who are less familiar with the tagless-final approach and more familiar with standard algebraic data type representation.


It is recommended to use opam for package management. To install pyre-ast with opam, you can run:

opam install pyre-ast


It is recommended to use dune as your build system. To use pyre-ast in your dune project, you can add pyre-ast to the libraries stanza in your dune file. For example,

  (name mylib)
  (libraries pyre-ast))

Documentation of this library can be found here.


It is recommended to use a local switch for development:

$ git clone
$ cd pyre-ast
$ opam switch create ./ 4.14.0 --deps-only --with-test
$ dune build @install  # Build the library
$ dune test            # Run tests

Dependencies (7)

  1. ppx_make >= "0.2.1"
  2. ppx_deriving >= "5.2.1"
  3. ppx_hash >= "v0.14.0"
  4. ppx_compare >= "v0.14.0"
  5. ppx_sexp_conv >= "v0.14.0"
  6. base >= "v0.14.1"
  7. dune >= "2.8"

Dev Dependencies (4)

  1. odoc with-doc
  2. cmdliner with-test & >= "1.1.0"
  3. sexplib with-test & >= "v0.14.0"
  4. stdio with-test & >= "v0.14.0"

Used by (1)

  1. opine




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