Gnarl is a small module for Python which allows defining classes with type-checked attributes, conforming to a predetermined schema.

Classes with Gnarl schemas can be used to:

• Type-check object attributes.
• Validate input data.
• Deserialize input data to application objects, with direct support for deserializing JSON.
• Serialize application objects to JSON.

Define a class, with a schema attached to it used to type-check the attributes:

>>> from gnarl import Schemed
>>> class Point(Schemed):
...   __schema__ = { "x": int, "y": int }
...
>>>

Now values can be created, using keyword arguments to set the values of the attributes. Note how the attributes can be accessed normally:

>>> location = Point(x=-3, y=5)
>>> location.x, location.y
(-3, 5)
>>>

Attributes are type-checked:

>>> location.x = 6  # Succeds
>>> location.x = "invalid value"  # Fails
Traceback (most recent call last):
   ...
gnarl.SchemaError: 'invalid value' should be instance of <class 'int'>
>>> location.x, location.y  # Values remain unchanged
(6, 5)
>>>

Last, but not least, conversion to and from JSON is automatically supported:

>>> json_text = location.to_json(sort_keys=True)
>>> json_text
'{"x": 6, "y": 5}'
>>> value = Point.from_json(json_text)
>>> value.__class__.__name__
'Point'
>>>

The stable releases are uploaded to PyPI, so you can install them and upgrade using pip:

pip install gnarl

Alternatively, you can install development versions —at your own risk— directly from the Git repository:

pip install -e git://github.com/aperezdc/gnarl

The documentation for Gnarl is available at:

http://gnarl.readthedocs.io/en/latest

Note that the documentation is work in progress. In the meanwhile, you may want to read the source code of the module itself for additional insight, or even better, the code of projects using the module.

If you want to contribute, please use the usual GitHub workflow:

1. Clone the repository.
2. Hack on your clone.
3. Send a pull request for review.

If you do not have programming skills, you can still contribute by reporting issues that you may encounter.

The following projects make use of Gnarl |gnarl-icon|:

• intheam-python
• pebbletime-python

(If you use it, please do not hesitate in editing this file and add a line to this list.)