Proof of concept to require trailing commas in `flake8`

.gitignore

*.pyc
build/
dist/
flake8_commas.egg-info
flake8_commas/

README.md

We are interested in supporting trailing commas via flake8 but need to verify that this can be easily achieved via AST tokens. This repo is a proof of concept for said verification.

Conclusion: It can be done via tokens but it will be complicated since there is no distinction of brackets.

https://hg.python.org/cpython/file/2.7/Lib/tokenize.py#l87

bad.py

hello = {
    'world': True
}

flake8_commas.py

# Load in dependencies
import ast


# Define our linter
class CommaLinter(object):
    """Flake8 extension to lint for/against trailing commas"""
    # TODO: Can we really support `disallow` as well?
    name = 'flake8_commas'
    # TODO: Figure out good foundry versioning system...
    version = '1.0.0'
    _code = 'C902'

    def __init__(self, tree, filename):
        """Handle incoming AST and filename"""
        # Save filename for later
        self.filename = filename

    def run(self):
        """Walk through the tree and find any multiline params/tuples/lists/dicts without a trailing comma"""
        # Walk our AST
        # https://docs.python.org/2/library/token.html
        # https://hg.python.org/cpython/file/2.7/Lib/tokenize.py
        for node in ast.walk(self.tree):
            # If we are on a dict
            # TODO: Handle params, tuples, lists, and dicts
            if isinstance(node, ast.Dict):
                # DEV: We allow ourselves to keep on walking as there might be nested dicts
                # TODO: What's a store/load?
                print node.__dict__
        return []

install.sh

#!/usr/bin/env bash
# Echo commands and exit on first error
set -e
set -x

# Create a folder to install with
mkdir flake8_commas
ln -s ../flake8_commas.py flake8_commas/__init__.py

# Install our dependencies
pip install -r requirements.txt

# Load our module
python setup.py develop

requirements.txt

flake8==2.4.0

setup.py

from setuptools import setup, find_packages


setup(
    name='flake8_commas',
    version='1.0.0',
    description='Flake8 extension to lint for/against trailing commas',
    # long_description=open('README.rst').read(),
    keywords=[

    ],
    author='Todd Wolfson',
    author_email='todd@twolfson.com',
    url='',
    download_url='none/archive/master.zip',
    packages=find_packages(),
    license='UNLICENSE',
    install_requires=open('requirements.txt').readlines(),
    entry_points={
        # TODO: Figure out valid extension number
        'flake8.extension': ['C902 = flake8_commas:CommaLinter'],
    },
    # https://pypi.python.org/pypi?%3Aaction=list_classifiers
    classifiers=[
        'Development Status :: 3 - Alpha',
        'Intended Audience :: Developers',
        'License :: Public Domain',
        'Operating System :: OS Independent',
        'Programming Language :: Python'
    ]
)