Flake8 Extension to enforce better comma placement.

Usage

If you are using flake8 it's as easy as:

pip install flake8-commas

Now you can avoid those annoying merge conflicts on dictionary and list diffs.

Errors

Different versions of python require commas in different places. Ignore the errors for languages you don't use in your flake8 config:

Code	message
C812	missing trailing comma
C813	missing trailing comma in Python 3
C814	missing trailing comma in Python 2
C815	missing trailing comma in Python 3.5+
C816	missing trailing comma in Python 3.6+
C818	trailing comma on bare tuple prohibited
C819	trailing comma prohibited

Examples

lookup_table = {
    'key1': 'value',
    'key2': 'something'  # <-- missing a trailing comma
}

json_data = json.dumps({
    "key": "value",
}),                      # <-- incorrect trailing comma. json_data is now a tuple. Likely by accident.

Related tools

You may wish to consider one of the following tools alongside or instead of flake8-commas.

For automatic insertion of commas, though noting that these tools may implement different rules around where commas should be placed:

• black, the uncompromising Python code formatter
• add-trailing-comma, which can do comma insertion automatically