jsonschema

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)
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
- format, though the schema does not mandate it anyhow. Note however that by default, jsonschema is strict about unknown properties, so using format without passing unknown_property="skip" to a validator will raise a SchemaError until it is properly supported.

Validation that reports all errors, rather than short-circuiting on the first validation error (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, extensibile, strict! and has as clean of an API as is feasible

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 03, with preparations for draft 04 underway. The current plan is likely to have the validators in this module take a version argument, which will allow support for future versions. Whether draft 03 will remain the default version used or not is undecided, so to be safe, explicitly declare which version of the schema you will be validating with. You can do so by passing version=jsonschema.DRAFT_3 into jsonschema.Validator (and similarly validate).

A Quick Word on uniqueItems

Validating schemas with the uniqueItems property can leave you open to algorithmic complexity attacks. This may change in the future. For now, jsonschema will warn you if you use uniqueItems without using the Securetypes module, but will proceed anyhow if it couldn't be imported.

TODO

Optimize extends to prevent doing double work
Implement some time of prioritizing, to allow quick validation checks to run first

Contributing and Contact Info

I'm Julian Berman :).

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