Convert a JSON schema to a python class

Question

Is there a python library for converting a JSON schema to a python class definition, similar to jsonschema2pojo -- https://github.com/joelittlejohn/jsonschema2pojo -- for Java?

Answer 1

So far the closest thing I've been able to find is warlock, which advertises this workflow:

Build your schema

>>> schema = {
    'name': 'Country',
    'properties': {
        'name': {'type': 'string'},
        'abbreviation': {'type': 'string'},
    },
    'additionalProperties': False,
}

Create a model

>>> import warlock
>>> Country = warlock.model_factory(schema)

Create an object using your model

>>> sweden = Country(name='Sweden', abbreviation='SE')

However, it's not quite that easy. The objects that Warlock produces lack much in the way of introspectible goodies. And if it supports nested dicts at initialization, I was unable to figure out how to make them work.

To give a little background, the problem that I was working on was how to take Chrome's JSONSchema API and produce a tree of request generators and response handlers. Warlock doesn't seem too far off the mark, the only downside is that meta-classes in Python can't really be turned into 'code'.

Other useful modules to look for:

• jsonschema - (which Warlock is built on top of)
• valideer - similar to jsonschema but with a worse name.
• bunch - An interesting structure builder thats half-way between a dotdict and construct

If you end up finding a good one-stop solution for this please follow up your question - I'd love to find one. I poured through github, pypi, googlecode, sourceforge, etc.. And just couldn't find anything really sexy.

For lack of any pre-made solutions, I'll probably cobble together something with Warlock myself. So if I beat you to it, I'll update my answer. :p

Answer 2

python-jsonschema-objects is an alternative to warlock, build on top of jsonschema

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

Usage:

Sample Json Schema

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"]
} '''

Converting the schema object to class

 import python_jsonschema_objects as pjs
 import json
 schema = json.loads(schema)   
 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  

Validation :

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

But problem is , it is still using draft4validation while jsonschema has moved over draft4validation , i filed an issue on the repo regarding this . Unless you are using old version of jsonschema , the above package will work as shown.

Answer 3

I just created this small project to generate code classes from json schema, even if dealing with python I think can be useful when working in business projects:

pip install jsonschema2popo

running following command will generate a python module containing json-schema defined classes (it uses jinja2 templating)

jsonschema2popo -o /path/to/output_file.py /path/to/json_schema.json

more info at: https://github.com/frx08/jsonschema2popo

Answer 4

datamodel-code-generator is a cli code generator that can build pydantic models and dataclasses.dataclass from various sources including JSON schema.

At the time of writing it has a lot more users according to GitHub than the libraries in other answers

Example usage to generate python dataclasses from a json schema:

datamodel-codegen --input ./<your-data-here>.json --input-file-type jsonschema --output <your-data-here>.py --output-model-type dataclasses.dataclass