This is a pre-production deployment of Warehouse, however changes made here WILL affect the production instance of PyPI.
Latest Version Dependencies status unknown Test status unknown Test coverage unknown
Project Description
_          _       _     _
\\        (_)     | |   | |
 \\   _ __ _  __ _| |__ | |_ __ _ _ __ _ __ _____      __
  \\ | '__| |/ _` | '_ \| __/ _` | '__| '__/ _ \ \ /\ / /
   \\| |  | | (_| | | | | || (_| | |  | | | (_) \ V  V /
    \\_|  |_|\__, |_| |_|\__\__,_|_|  |_|  \___/ \_/\_/
             __/ |

This library provides a language for concise higher-order annotations for Python programs, inspired by the syntax for higher-order contracts and types in advanced languages. Functionality akin to contract checking, type checking, and type inference is a work-in-progress.

This project has a “duck-typed” status: Whatever you can use it for, it is ready for :-)

Here is a more concrete list of implemented and intended features:

  • yes - Definition of a the language.
  • yes - Parsing and printing.
  • yes - Run-time monitoring of adherence for monomorphic annotations.
  • upcoming - Monitoring of adherence for polymorphic annotations.
  • upcoming - Generation of constraints between annotations in a program.
  • upcoming - Best-effort inference of suitable annotations.
  • upcoming - More precise annotations to support full higher-order design-by-contract.

The Annotations

This language is built from the following concepts:

  • Named types: int, long, float, complex, str, unicode, file, YourClassNameHere, …
  • Lists: [int], [[long]], …
  • Tuples: (int, long), (float, (int, Regex)), …
  • Dictionaries: {string: float}, { (str, str) : [complex] }, …
  • Unions: int|long|float, str|file, …
  • “Anything goes”: ??
  • Functions, after which this library is named :-)
    • str -> int
    • (int) -> int
    • (int, int) -> int
    • ( (int, int) ) -> int
    • ( str|file ) -> SomeClass
    • (int, *[str]) -> [(str, int)]
    • (int, *[int], **{int: str}) -> str
  • Objects: object(self_type, field1: int, field2: str, ...)
  • Polymorphic types (where ~a, ~b, ~c range over any other type. Syntax subject to change; no preference really)
    • ~a -> ~a
    • [~a] -> [~a]
    • ( (~a, ~b) ) -> ~a

Run-time checking

The module typelanguage.enforce contains functions for using these annotations as run-time monitors.

Applied directly:

>>> check('{string: int}', {"hello" : "there"})

Wrapping a function to protect it from funky input is more interesting. For example, putting better error checking on Python’s unicode/str interactions (at least in Python 2)

>>> '\xa3'.encode('utf-8')
UnicodeDecodeError: 'ascii' codec can't decode byte 0xa3 in position 0: ordinal not in range(128)

>>> @guard('unicode -> str')
... def safe_encode(s):
...    return s.encode('utf-8')

>>> safe_encode(u'hello')
>>> safe_encode('\xa3')
TypeError: Type check failed: ? does not have type unicode

If you are familiar with notions of “blame” for higher-order contracts, pull-requests welcome :-)

Inferring Annotations

Inference is a work-in-progress, definitely planned, and almost certainly will always be “best effort” only. It works like so:

  1. By traversing the code, we can discover a bunch of constraints between different missing annotations.
  2. Some of these constraints are going to be very easy to solve, so we can just propagate the results.
  3. Some of these constraints are not going to be practical to try to solve, so we can just drop them or insert some enforcement code if we like.

More to explore

There are many other projects that check contracts or types for Python in some way. They are all different, many are prototypes or research projects, and none seem to serve the need that motivates this library. Still, check them out!

And there are cool things happening in other dynamic languages!

And this library draw inspiration from such a huge amount of academic work it cannot possibly all be mentioned, but special thanks to these research efforts


Release History

Release History


This version

History Node

TODO: Figure out how to actually get changelog content.

Changelog content for this version goes here.

Donec et mollis dolor. Praesent et diam eget libero egestas mattis sit amet vitae augue. Nam tincidunt congue enim, ut porta lorem lacinia consectetur. Donec ut libero sed arcu vehicula ultricies a non tortor. Lorem ipsum dolor sit amet, consectetur adipiscing elit.

Show More

Download Files

Download Files

TODO: Brief introduction on what you do with files - including link to relevant help section.

File Name & Checksum SHA256 Checksum Help Version File Type Upload Date
rightarrow-0.4.tar.gz (17.5 kB) Copy SHA256 Checksum SHA256 Source Mar 16, 2013

Supported By

WebFaction WebFaction Technical Writing Elastic Elastic Search Pingdom Pingdom Monitoring Dyn Dyn DNS HPE HPE Development Sentry Sentry Error Logging CloudAMQP CloudAMQP RabbitMQ Heroku Heroku PaaS Kabu Creative Kabu Creative UX & Design Fastly Fastly CDN DigiCert DigiCert EV Certificate Rackspace Rackspace Cloud Servers DreamHost DreamHost Log Hosting