deb-python-jsonschema/docs/creating.rst

Creating or Extending Validator Classes

jsonschema.validators

create

Create a new validator class.

argument dict meta_schema

the meta schema for the new validator class

argument dict validators

a mapping from names to callables, where each callable will validate the schema property with the given name.

Each callable should take 4 arguments:

1. a validator instance,
2. the value of the property being validated within the instance
3. the instance
4. the schema

argument str version

an identifier for the version that this validator class will validate. If provided, the returned validator class will have its __name__ set to include the version, and also will have validates automatically called for the given version.

argument dict default_types

a default mapping to use for instances of the validator class when mapping between JSON types to Python types. The default for this argument is probably fine. Instances can still have their types customized on a per-instance basis.

returns

a new jsonschema.IValidator class

extend

Create a new validator class by extending an existing one.

argument jsonschema.IValidator validator

an existing validator class

argument dict validators

a mapping of new validator callables to extend with, whose structure is as in create.

Note

Any validator callables with the same name as an existing one will (silently) replace the old validator callable entirely, effectively overriding any validation done in the "parent" validator class.

If you wish to instead extend the behavior of a parent's validator callable, delegate and call it directly in the new validator function by retrieving it using OldValidator.VALIDATORS["validator_name"].

argument str version

a version for the new validator class

returns

a new jsonschema.IValidator class

Note

Meta Schemas

The new validator class will have its parent's meta schema.

If you wish to change or extend the meta schema in the new validator class, modify META_SCHEMA directly on the returned class. Note that no implicit copying is done, so a copy should likely be made before modifying it, in order to not affect the old validator.

validator_for

Retrieve the validator class appropriate for validating the given schema.

Uses the $schema property that should be present in the given schema to look up the appropriate validator class.

argument schema

the schema to look at

argument default

the default to return if the appropriate validator class cannot be determined. If unprovided, the default is to return Draft4Validator

validates

Creating Validation Errors

Any validating function that validates against a subschema should call ValidatorMixin.descend, rather than ValidatorMixin.iter_errors. If it recurses into the instance, or schema, it should pass one or both of the path or schema_path arguments to ValidatorMixin.descend in order to properly maintain where in the instance or schema respsectively the error occurred.