PyonR

PyonR (pronounced "Pioneer") is an implementation of the Python programming language for the Racket platform.

Installation:

Before installing PyonR, you will need to have Racket v6.01 or above and optionally Python 2.7.

You can install PyonR from DrRacket's Install Package dialog box with git://github.com/pedropramos/PyonR as the package source. Make sure you change the package name to python.

Alternatively, you can install it with the raco tool by running:

raco pkg install -n python git://github.com/pedropramos/PyonR

Updating:

You can update the currently installed version with DrRacket's Package Manager, or alternatively with the following raco command:

raco pkg update python

Use:

To use PyonR with DrRacket, simply replace #lang racket with #lang python.

Limitations:

PyonR currently supports most of the Python language as specified by version 2.7, except for a few constructs (most notably the del and with statements, decorators and the super function for constructors) and some missing methods on built-in types.

Extensions to the Python language:

Importing modules from Python 2.7

If you have Python 2.7 installed on your system, you can import its modules using Python's importing statements, but replacing the import keyword by cpyimport. This allows you to access Python's full standard library as well any third-party libraries you have installed, such as NumPy or SciPy.

For a demonstration, check out the examples at examples/numpy_arrays and examples/datetime.

UPDATE (18/11/2014): Many users have reported issues with CPython's VM during PyonR's installation, therefore the cpyimport import must now be manually enabled from Racket after installing PyonR. To do so, require the python/config module and run (enable-cpyimport!). You only need to do this once. If you turn out to have any issues after this, you can disable it by running (disable-cpyimport!).

Importing modules from Racket:

You can import Racket modules by using Python's import statements and specifying the module's require specification withing string quotes. For instance, to access Racket's cons, car and cdr functions from Python, one could type one of the following:

• import "racket" as rkt
• from "racket" import cons, car, cdr
• from "racket" import *

Keep in mind that Python's rules for identifier names are stricter than Racket's. Therefore, PyonR resorts to name mangling for identifiers whose names are not allowed in Python. For instance, the number->string function would have to be imported as:

• from "racket" import number_TO_string

We provide a builtin Python module called name_mangling with the function mangle which returns a Python mangled name, given the original Racket name as argument.

Predicate dispatching

PyonR supports an extensible predicate dispatch mechanism to map Racket predicates to Python types. This is particularly aimed for giving a Python feel to imported Racket datatypes, since their functionality is typically spread among predicates, constructors, getters, setters and assorted functions. This way, you can map a datatype's predicate to a user-defined Python class such that getters and setters are available as properties and other functions are available as methods.

This functionality is provided by the builtin Python module predicates which defines the following functions:

• set_predicate(pred, type) - sets a mapping between the pred predicate and type.
• set_predicate(pred) - removes pred's mapping.
• define_subtype(pred, parent) - defines the pred predicate as a subtype of parent predicate, so that pred is dispatched before parent.

For a demonstration, check out the example at examples/rosetta.