Adding a custom 'type'

[will...@gmail.com]

I'm not sure if this is possible, but I'm attempting to add a new 'type' called 'file', which validates the instance value by verifying that a file exists by that name.

I'm attempting to use the 'redefine' method of a TypeChecker to create a new 'type'.

import os

from jsonschema import validators, Draft4Validator

schema = {
    'type': 'file'
}

checker = Draft4Validator.TYPE_CHECKER.redefine("file", lambda _, value: os.path.exist(value))
Validator = validators.extend(Draft4Validator, type_checker=checker)

Validator.check_schema(schema)

When I run this however, I get:

Traceback (most recent call last):
  File "test_schema.py", line 24, in test_combination
    Validator.check_schema(schema)
  File "C:\python\lib\site-packages\jsonschema\validators.py", line 235, in check_schema
    raise SchemaError.create_from(error)
jsonschema.exceptions.SchemaError: 'file' is not valid under any of the given schemas

Failed validating 'anyOf' in metaschema['properties']['type']:
    {'anyOf': [{'$ref': '#/definitions/simpleTypes'},
               {'items': {'$ref': '#/definitions/simpleTypes'},
                'minItems': 1,
                'type': 'array',
                'uniqueItems': True}]}

It looks like redefine isn't the right way to go about this, is there another way to add a custom type?

[Julian Berman]

In general the metaschemas these days restrict the types to just the predefined names -- so TypeCheckers are mainly for changing the mapping to the existing types more than adding new ones.

What you'd need to do here is to also add the file type to the metaschema you're extending, or alternatively, using "format" instead of "type" for the custom behavior is a bit smoother for these sorts of things.

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[will...@gmail.com]

I haven't tried the 'format' option yet, but your recommendation about adding to the metaschema seems to have fixed it:

from os.path import exists

from jsonschema import validators, Draft4Validator


schema = {'type': 'file'}

Draft4Validator.META_SCHEMA['definitions']['simpleTypes']['enum'].append('file')

checker = Draft4Validator.TYPE_CHECKER.redefine("file", lambda _, value: exists(value))

Validator = validators.extend(Draft4Validator, type_checker=checker)
Validator.check_schema(schema)

validator = Validator(schema=schema)
validator.validate('real.txt')
validator.validate('fake.txt')

Traceback (most recent call last):

  File "test_schema.py", line 21, in test_combination
    validator.validate('fake.txt')
  File "C:\python\lib\site-packages\jsonschema\validators.py", line 282, in validate
    raise error
jsonschema.exceptions.ValidationError: 'fake.txt' is not of type 'file'

Failed validating 'type' in schema:
    {'type': 'file'}

On instance:
    'fake.txt'

Thanks!

[Michał Stolarczyk]

hi,

How do I use the new custom Validator with jsonschema.validate function?

This is what I have:

from os.path import exists

import jsonschema

def f(checker, instance):

    return exists(instance)

jsonschema.Draft6Validator.META_SCHEMA['definitions']['simpleTypes']['enum'].append('path')

checker = jsonschema.Draft6Validator.TYPE_CHECKER.redefine("path", f)

myValidator = validators.extend(jsonschema.Draft6Validator, type_checker=checker)

pvalidator = myValidator(schema={'type': 'path'})

schema = _read_schema("/path/to/schema.yaml")  

jsonschema.validate(p2, schema, cls= pvalidator)

calling the function results in a TypError: 

TypeError: 'Validator' object is not callable

Thanks in advance!

Michal