jsonschema

jsonschema is an implementation of JSON Schema (currently in Draft 3) for Python (supporting 2.6+ including Python 3).

>>> from jsonschema import validate

>>> # A sample schema, like what we'd get from json.load()
>>> schema = {
...     "type" : "object",
...     "properties" : {
...         "price" : {"type" : "number"},
...         "name" : {"type" : "string"},
...     },
... }

>>> # If no exception is raised by validate(), the instance is valid.
>>> validate({"name" : "Eggs", "price" : 34.99}, schema)

>>> validate(
...     {"name" : "Eggs", "price" : "Invalid"}, schema
... )                                   # doctest: +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
    ...
ValidationError: 'Invalid' is not of type 'number'

Features

• Support for Draft 3 of the Schema with the exception of

  • Non-JSON Pointer $ref, and extends that use them

• Lazy validation that can iteratively report all validation errors.

>>> from jsonschema import Draft3Validator
>>> schema = {
...     "type" : "array",
...     "items" : {"enum" : [1, 2, 3]},
...     "maxItems" : 2,
... }
>>> v = Draft3Validator(schema)
>>> for error in sorted(v.iter_errors([2, 3, 4]), key=str):
...     print(error)
4 is not one of [1, 2, 3]
[2, 3, 4] is too long

• Small and extensible
• Programmatic querying of which properties or items failed validation.

>>> from jsonschema import ErrorTree, Draft3Validator
>>> schema = {
...     "type" : "array",
...     "items" : {"type" : "number", "enum" : [1, 2, 3]},
...     "minItems" : 3,
... }
>>> instance = ["spam", 2]
>>> v = Draft3Validator(schema)
>>> tree = ErrorTree(v.iter_errors(instance))

>>> sorted(tree.errors)
['minItems']

>>> 0 in tree
True

>>> 1 in tree
False

>>> sorted(tree[0].errors)
['enum', 'type']

>>> print(tree[0].errors["type"].message)
'spam' is not of type 'number'

Schema Versioning

JSON Schema is, at the time of this writing, seemingly at Draft 3, with preparations for Draft 4 underway. As of right now, Draft 3 is the only supported version, and the default when validating. Preparations for implementing some Draft 4 support are in progress.

Release Notes

v0.7 introduces a number of changes.

The most important one is that the Validator class is now deprecated.

In its place is the Draft3Validator class (soon to be accompanied by others for other supported versions). This class accepts a schema when initializing, so that the new interface is:

validator = Draft3Validator(my_schema)
validator.validate(some_instance)

Also, no meta-validation is done. If you want to check if a schema is valid, use the check_schema classmethod (i.e. use Draft3Validator.check_schema(a_maybe_valid_schema)).

The validate function of course still exists and continues to work as it did before:

from jsonschema import validate
validate(my_instance, my_schema)

There's just one exception: the meta_validate argument is deprecated, and meta-validation will now always be done. If you don't want to have it done, construct a validator directly as above.

One last thing that is present is partial support for $ref, at least for JSON Pointer refs. Full support should be coming soon.

As always, if you find any bugs, please file a ticket.

Running the Test Suite

jsonschema uses the wonderful Tox for its test suite. (It really is wonderful, if for some reason you haven't heard of it, you really should use it for your projects).

Assuming you have tox installed (perhaps via pip install tox or your package manager), just run tox in the directory of your source checkout to run jsonschema's test suite on all of the versions of Python jsonschema supports. Note that you'll need to have all of those versions installed in order to run the tests on each of them, otherwise tox will skip (and fail) the tests on that version.

Contributing

I'm Julian Berman.

jsonschema is on GitHub.

Get in touch, via GitHub or otherwise, if you've got something to contribute, it'd be most welcome!

You can also generally find me on Freenode (nick: tos9) in various channels, including #python.