Skip to main content
This is a pre-production deployment of Warehouse. Changes made here affect the production instance of PyPI (
Help us improve Python packaging - Donate today!

Lightweight module to define serializable, schema-validated classes

Project Description

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

Classes with Lasso 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 lasso 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):
schema.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__


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

pip install lasso

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

pip install -e git://


The documentation for Lasso is available at:

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 Lasso :

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

Release History

History Node


History Node


History Node


This version
History Node


History Node


History Node


History Node


History Node


Download Files

Download the file for your platform. If you're not sure which to choose, learn more about installing packages.

Filename, Size & Hash SHA256 Hash Help File Type Python Version Upload Date
(5.0 kB) Copy SHA256 Hash SHA256
Source None Mar 14, 2016

Supported By

Elastic Elastic Search Pingdom Pingdom Monitoring Dyn Dyn DNS Sentry Sentry Error Logging CloudAMQP CloudAMQP RabbitMQ Kabu Creative Kabu Creative UX & Design Google Google Cloud Servers Fastly Fastly CDN StatusPage StatusPage Statuspage DigiCert DigiCert EV Certificate