Mushmallow

Reformat Marshmallow schemas.

I wrote this tool to handle the transformation of implicit to explicit metadata fields in Marshmallow schemas, as per marshmallow-code/marshmallow#1702.

For example:

from marshmallow import Schema, fields

class MySchema(Schema):
    my_field = fields.String(
        allow_none=True,
        description="This is my field"
    )

gets transformed to

from marshmallow import Schema, fields

class MySchema(Schema):
    my_field = fields.String(
        allow_none=True,
        metadata={
            "description": "This is my field",
        },
    )

(with --fix-kwargs-for-marshmallow-4 specified`).

The tool can/will:

• Wrap lines at a configurable line length (a bit like black)
• Standardize on double quoted strings (a bit like black)
• Standardize on how multi-line strings are formatted
• Add trailing commas (a bit like black)
• Optionally sort keyword arguments/dictionary keys alphabetically
• Optionally produce a diff rather than modifiy the files (a bit like black)

See --help for the full list of options. See the unit tests (particularly test_core.py to see the transformations that are applied.

Installation and running

1. Checkout the repo
2. make venv
3. venv/bin/python -m mushmallow <options> <path to file>

Note that this tool is not available on PyPi at the time of writing.

Development

Run make check to run full CI. Run make check-<thing> to run specific targets. See the Makefile.

Limitations

• I hacked this together to get it working for the schemas I need to transform.
• It is not exhaustively tested and there maybe cases that simply don't work (probably around the AST handling).
• Only tested against Python3.11.
• Identifies schema definitions based on sub-classes of classes suffixed with 'Schema'.