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

  • $ref, and extends that use $refs

• Lazy validation that can iteratively report all validation errors.

>>> from jsonschema import Validator
>>> schema = {
...     "type" : "array",
...     "items" : {"enum" : [1, 2, 3]},
...     "maxItems" : 2,
... }
>>> v = Validator()
>>> for error in sorted(v.iter_errors([2, 3, 4], schema), 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, Validator
>>> schema = {
...     "type" : "array",
...     "items" : {"type" : "number", "enum" : [1, 2, 3]},
...     "minItems" : 3,
... }
>>> instance = ["spam", 2]
>>> v = Validator()
>>> tree = ErrorTree(v.iter_errors(instance, schema))

>>> 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. The Validator class and validate function take a version argument that you can use to specify what version of the Schema you are validating under.

As of right now, Draft 3 (jsonschema.DRAFT_3) is the only supported version, and the default when validating. Whether it will remain the default version in the future when it is superceeded is undecided, so if you want to be safe, explicitly declare which version to use when validating.

Release Notes

• Preliminary support for programmatic access to error details (Issue #5). There are certainly some corner cases that don't do the right thing yet, but this works mostly.

  In order to make this happen (and also to clean things up a bit), a number of deprecations are necessary:

  • stop_on_error is deprecated in Validator.__init__. Use Validator.iter_errors() instead.
  • number_types and string_types are deprecated there as well. Use types={"number" : ..., "string" : ...} instead.
  • meta_validate is also deprecated, and instead is now accepted as an argument to validate, iter_errors and is_valid.

• A bugfix or two

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.

License

Copyright (c) 2011 Julian Berman

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.