typed_ast is a Python 3 package that provides a Python 2.7 and Python 3
parser similar to the standard ast library. Unlike ast, the parsers in
typed_ast include PEP 484 type
comments and are independent of the version of Python under which they are run.
The typed_ast parsers produce the standard Python AST (plus type comments),
and are both fast and correct, as they are based on the CPython 2.7 and 3.6
parsers. typed_ast runs on Python 3.3-3.6 on Linux, OS X and Windows.
This project is a drop-in replacement for the builtin ast module. It is
intended to be bug-for-bug compatible and behave identically, except for the
presence of a few additional fields on the returned classes and a few
additional optional arguments to the parse call. Therefore, typed_ast will
not accept any bugfixes for bugs in ast -- they should be fixed upstream
instead. To avoid feature bloat, any new features for typed_ast should have
the potential to be broadly useful and not be built just for one niche usecase
or in a manner such that only one project can use them.
The ast3 parser produces the AST from the latest version of Python 3
(currently Python 3.6). When new versions of Python 3 are released, it will be
updated to match any changes in their AST. (For rationale and technical
details, see here.) The AST it currently produces is described in
ast3/Parser/Python.asdl. If you wish to limit
parsing to older versions of Python 3, ast3 can be configured to to give a
SyntaxError for new syntax features introduced beyond a given Python version.
For more information, see the module docstring in
typed_ast/ast3.py.
The ast27 parser tracks the standard Python 2.7 AST, which is expected to
never receive further updates. The AST it produces is described in
ast27/Parser/Python.asdl. For more information,
see the module docstring in typed_ast/ast27.py.
typed_ast also provides a conversions module which converts ast27 ASTs
into ast3 ASTs. This functionality is somewhat experimental, however. For
more information, see the py2to3 docstring in
typed_ast/conversions.
Note: as these parsers consider type comments part of the grammar, incorrectly placed type comments are considered syntax errors.
To update typed_ast for new major Python releases, see update_process.md.
To make a new typed_ast release, see release_process.md.