python-jsonschema-objects 0.0.13

An object wrapper for JSON Schema definitions

What

python-jsonschema-objects provides an automatic class-based binding to JSON schemas for use in python.

For example, given the following schema:

{
    "title": "Example Schema",
    "type": "object",
    "properties": {
        "firstName": {
            "type": "string"
        },
        "lastName": {
            "type": "string"
        },
        "age": {
            "description": "Age in years",
            "type": "integer",
            "minimum": 0
        },
        "dogs": {
            "type": "array",
            "items": {"type": "string"},
            "maxItems": 4
        },
        "gender": {
            "type": "string",
            "enum": ["male", "female"]
        },
        "deceased": {
            "enum": ["yes", "no", 1, 0, "true", "false"]
            }
    },
    "required": ["firstName", "lastName"]
}

jsonschema-objects can generate a class based binding. Assume here that the schema above has been loaded in a variable called schema:

>>> import python_jsonschema_objects as pjs
>>> builder = pjs.ObjectBuilder(schema)
>>> ns = builder.build_classes()
>>> Person = ns.ExampleSchema
>>> james = Person(firstName="James", lastName="Bond")
>>> james.lastName
u'Bond'
>>> james
<example_schema lastName=Bond age=None firstName=James>

Validations will also be applied as the object is manipulated.

>>> james.age = -2
python_jsonschema_objects.validators.ValidationError: -4 was less
or equal to than 0

The object can be serialized out to JSON:

>>> james.serialize()
'{"lastName": "Bond", "age": null, "firstName": "James"}'

Why

Ever struggled with how to define message formats? Been frustrated by the difficulty of keeping documentation and message definition in lockstep? Me too.

There are lots of tools designed to help define JSON object formats, foremost among them JSON Schema. JSON Schema allows you to define JSON object formats, complete with validations.

However, JSON Schema is language agnostic. It validates encoded JSON directly - using it still requires an object binding in whatever language we use. Often writing the binding is just as tedious as writing the schema itself.

This avoids that problem by auto-generating classes, complete with validation, directly from an input JSON schema. These classes can seamlessly encode back and forth to JSON valid according to the schema.

Other Features

The ObjectBuilder can be passed a dictionary specifying ‘memory’ schemas when instantiated. This will allow it to resolve references where the referenced schemas are retrieved out of band and provided at instantiation.

For instance:

{
    "title": "Address",
    "type": "string"
}

{
    "title": "AddlPropsAllowed",
    "type": "object",
    "additionalProperties": true
}

{
    "title": "Other",
    "type": "object",
    "properties": {
        "MyAddress": {"$ref": "memory:Address"}
    },
    "additionalProperties": false
}

Generated wrappers can also properly deserialize data representing ‘oneOf’ relationships, so long as the candidate schemas are unique.

{
    "title": "Age",
    "type": "integer"
}

{
    "title": "OneOf",
    "type": "object",
    "properties": {
        "MyData": { "oneOf":[
            {"$ref": "memory:Address"},
            {"$ref": "memory:Age"}
            ]
        }
    },
    "additionalProperties": false
}

Installation

pip install python_jsonschema_objects

Tests

Tests are managed using the excellent Tox. Simply pip install tox, then tox.

Changelog

0.0.13 - Lazily build object classes. Allows low-overhead use of jsonschema validators.

0.0.12 - Support “true” as a value for ‘additionalProperties’

0.0.11 - Generated wrappers can now properly deserialize data representing ‘oneOf’ relationships, so long as the candidate schemas are unique.

0.0.10 - Fixed incorrect checking of enumerations which previously enforced that all enumeration values be of the same type.

0.0.9 - Added support for ‘memory:’ schema URIs, which can be used to reference externally resolved schemas.

0.0.8 - Fixed bugs that occurred when the same class was read from different locations in the schema, and thus had a different URI

0.0.7 - Required properties containing the ‘@’ symbol no longer cause build_classes() to fail.

0.0.6 - All literals now use a standardized LiteralValue type. Array validation actually coerces element types. as_dict can translate objects to dictionaries seamlessly.

0.0.5 - Improved validation for additionalItems (and tests to match). Provided dictionary-syntax access to object properties and iteration over properties.

0.0.4 - Fixed some bugs that only showed up under specific schema layouts, including one which forced remote lookups for schema-local references.

0.0.3b - Fixed ReStructuredText generation

0.0.3 - Added support for other array validations (minItems, maxItems, uniqueItems).

0.0.2 - Array item type validation now works. Specifying ‘items’, will now enforce types, both in the tuple and list syntaxes.

0.0.1 - Class generation works, including ‘oneOf’ and ‘allOf’ relationships. All basic validations work.