Using input parameters for validation with marshmallow

Question

Is it possible to pass parameters to a marshmallow schema to use for validation on load?

I have the following schema:

from marshmallow import Schema, fields, validate

class ExampleSchema(Schema):
    tags = fields.List(fields.String(), validate=ContainsOnly(["a", "b", "c"]))

and I'm wondering whether, instead of typing "a", "b", "c", I could put parameters in there? Something like

class ExampleSchema(Schema, list_of_allowed_tags):
    tags = fields.List(fields.String(), validate=ContainsOnly(list_of_allowed_tags))

except this doesn't work because the following error comes up on import

NameError: name 'list_of_allowed_tags' is not defined

Any other ideas?

Answer 1

No, marshmallow Schema doesn't do that.

You can use a schema factory.

import marshmallow as ma


def example_schema_factory(list_of_allowed_tags):

    class ExampleSchema(ma.Schema):
        tags = ma.fields.List(
            ma.fields.String(),
            validate=ma.validate.ContainsOnly(list_of_allowed_tags)
        )

    return ExampleSchema