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'

• 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

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.

• Default for unknown types and properties is now to not error (consistent with the schema).
• Python 3 support
• Removed dependency on SecureTypes now that the hash bug has been resolved.
• "Numerous bug fixes" -- most notably, a divisibleBy error for floats and a bunch of missing typechecks for irrelevant properties.

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.