python

ATTENTION: This is a work in progress. Caveat emptor!

> \import calendar
> (display (\calendar.month 2022 09))
   September 2022
Mo Tu We Th Fr Sa Su
          1  2  3  4
 5  6  7  8  9 10 11
12 13 14 15 16 17 18
19 20 21 22 23 24 25
26 27 28 29 30

This module is an interface to Python for Gambit Scheme. It wraps and exposes the low-level CPython C API using the Gambit Scheme C FFI managing the CPython GIL and reference counting. It implements a Foreign Procedure Call mechanism which bridges the Gambit and CPython threading models. It also offers a convenient syntactic interface to write Python expressions in Scheme. This module allows the use of packages from the Python Package Index's (PyPI) repository of almost 400,000 packages.

For more details, see the preprint for our Scheme Workshop 2022 article here: A Foreign Function Interface between Gambit Scheme and CPython.

Getting started

Requirements

This module has a few mandatory requirements:

• You must have a recent version of Gambit compiled with the --enable-multiple-threaded-vms option.
• You must have a dynamically linked version of CPython >= 3.7 installed. This module will link against the CPython shared library.
• A Windows, Linux or macOS operating system (other OSes have not been tested but might work).

Installation

You can install and compile the program at the command-line as such:

gsi -install github.com/gambit/python
gsc github.com/gambit/python

or you can download and compile the module lazily by importing it from within gsi or any program compiled with the C backend:

(import (github.com/gambit/python))

In both cases, Gambit will download and compile the code. During compilation, the module will perform an automatic discovery of the installed CPython executable. Various C compiler options will be determined by introspection. This module will create a virtualenv to manage its packages.

Users can configure the compilation with environment variables:

• GAMBIT_PYTHON_EXECUTABLE is the path to the CPython executable (supersedes GAMBIT_PYTHON_VERSION)
• GAMBIT_PYTHON_VERSION is the CPython version to use (e.g. 3.7)
• GAMBIT_PYTHON_VENV is the directory where to put the virtualenv
• GAMBIT_PYTHON_DEBUG is a flag to show debug information (yes)

A default installation should work out of the box. By default, the Python virtualenv will be placed under ~~userlib/.venv${GAMBIT_PYTHON_VERSION}.

Usage

This module dynamically links to the CPython shared library. On some systems and configurations, you must preload the shared library. For example, on a Linux system you most probably need to invoke the gsi binary as such:

LD_PRELOAD=/path/to/Python-3.10.5/lib/libpython3.10.so gsi

To use the syntactic interface, you must import the (_six python) module. To use the low-level interface and instantiate the CPython VM, you must import the github.com/gambit/python module. Combined, these are:

(import (_six python)
        (github.com/gambit/python))

Installing packages

To install packages from PyPI, simply run (pip-install "package-name"). Advanced users can always load the virtual environment as they would any other, or use other packaging mechanisms if they wish.

Examples

The examples can be run as follows:

gsi github.com/gambit/python/examples/EXAMPLE_NAME_WITHOUT_SCM

So to run the requests example, you would do:

gsi github.com/gambit/python/examples/requests

Some examples require packages to be installed from the PyPI. These have to be manually installed using pip-install.

Testing

To test the module, run the following command:

gsi github.com/gambit/python/test

There is a specific test for memory leaks that you can run as:

gsi github.com/gambit/python/test/leaks

License and copyright

This software is distributed under the same terms as Gambit.

© Marc Feeley 2021-2022

© Marc-André Bélanger 2021-2022