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

>>> 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'


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

    • $ref, and extends that use $refs
  • Validation that reports all errors, rather than short-circuiting on the first validation error (toggleable, off by default):

    >>> from jsonschema import ValidationError, validate
    >>> schema = {
    ...     "type" : "array",
    ...     "items" : {"enum" : [1, 2, 3]},
    ...     "maxItems" : 2,
    ... }
    >>> try:
    ...     validate([2, 3, 4], schema, stop_on_error=False)
    ... except ValidationError as e:
    ...     print("Validation failed with errors:")
    ...     for error in sorted(e.errors):
    ...         print("    * " + error)
    Validation failed with errors:
        * 4 is not one of [1, 2, 3]
        * [2, 3, 4] is too long
  • Small and extensible

Note: the API is still considered unstable, though no major changes are expected.

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.

Contributing and Contact Info

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.

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