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Under the old implementation, ``` outer: A [inner] B C inner: B C [inner] ``` wouldn't get detected as the ambiguous grammar that it is, whereas ``` outer: A rest rest: [inner] B C inner: B C [inner] ``` would. This would manifest itself as non-determinism in the DFA state generation. See the discussion #62 on for a full explanation. This modifies the ambiguity detection to work on a broader class of issues, so it should now hopefully detect all cases where the given grammar is ambiguous. At some point, we could extend this logic to allow developers to optionally set precedence of grammar productions, which could resolve ambiguities, but that's not a strict requirement for parsing python.
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parso - A Python Parser
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.. image:: https://travis-ci.org/davidhalter/parso.svg?branch=master
:target: https://travis-ci.org/davidhalter/parso
:alt: Travis CI build status
.. image:: https://coveralls.io/repos/github/davidhalter/parso/badge.svg?branch=master
:target: https://coveralls.io/github/davidhalter/parso?branch=master
:alt: Coverage Status
.. image:: https://raw.githubusercontent.com/davidhalter/parso/master/docs/_static/logo_characters.png
Parso is a Python parser that supports error recovery and round-trip parsing
for different Python versions (in multiple Python versions). Parso is also able
to list multiple syntax errors in your python file.
Parso has been battle-tested by jedi_. It was pulled out of jedi to be useful
for other projects as well.
Parso consists of a small API to parse Python and analyse the syntax tree.
A simple example:
.. code-block:: python
>>> import parso
>>> module = parso.parse('hello + 1', version="3.6")
>>> expr = module.children[0]
>>> expr
PythonNode(arith_expr, [<Name: hello@1,0>, <Operator: +>, <Number: 1>])
>>> print(expr.get_code())
hello + 1
>>> name = expr.children[0]
>>> name
<Name: hello@1,0>
>>> name.end_pos
(1, 5)
>>> expr.end_pos
(1, 9)
To list multiple issues:
.. code-block:: python
>>> grammar = parso.load_grammar()
>>> module = grammar.parse('foo +\nbar\ncontinue')
>>> error1, error2 = grammar.iter_errors(module)
>>> error1.message
'SyntaxError: invalid syntax'
>>> error2.message
"SyntaxError: 'continue' not properly in loop"
Resources
=========
- `Testing <https://parso.readthedocs.io/en/latest/docs/development.html#testing>`_
- `PyPI <https://pypi.python.org/pypi/parso>`_
- `Docs <https://parso.readthedocs.org/en/latest/>`_
- Uses `semantic versioning <https://semver.org/>`_
Installation
============
pip install parso
Future
======
- There will be better support for refactoring and comments. Stay tuned.
- There's a WIP PEP8 validator. It's however not in a good shape, yet.
Known Issues
============
- `async`/`await` are already used as keywords in Python3.6.
- `from __future__ import print_function` is not ignored.
Acknowledgements
================
- Guido van Rossum (@gvanrossum) for creating the parser generator pgen2
(originally used in lib2to3).
- `Salome Schneider <https://www.crepes-schnaegg.ch/cr%C3%AApes-schn%C3%A4gg/kunst-f%C3%BCrs-cr%C3%AApes-mobil/>`_
for the extremely awesome parso logo.
.. _jedi: https://github.com/davidhalter/jedi