Piety is a notional operating system to be written in Python.

Motivation and Goals
Current Status
Roadmap
Dependencies
Python Versions
Tested Platform

Piety is a response to this impulse:

Today's operating systems and applications are bloated and complicated. Let's start over, and create a complete system that is small, easy to understand, and fun to program. And, let's build it all in our favorite language!

I am intrigued by the single user, single language, special hardware systems of the 1970s and 80s: Smalltalk, Lisp machines, Oberon (see doc/precursors.md). Those systems used a single programming language for both the applications and the operating system. You could use the language interpreter to inspect and manipulate any data in the running system. Changes to application and system code were effective immediately, without having to stop and restart the system.

Piety is an experiment to see if I can put together something similar today, but using a familiar programming language running on ordinary hardware. (For other projects in a similar spirit, again see doc/precursors.md.) I aim to produce, in Python, a simple but self-contained personal computer operating system. Let's see how far we can get with just Python. There is already a lot of work by others that we might be able to use or adapt (see doc/utilities.md).

For now, Piety runs in an ordinary Python interpreter session on a host operating system. Here is an explanation of the Piety design.

At this time, Piety provides cooperative multitasking, jobs that can be suspended and resumed, a Python- based shell with output redirection, a line editor, and a display editor.

The display editor includes a built-in shell and window manager, which together provide a minimal but self-contained programming environment within a single Python terminal session. It is the programmer's user interface to the Piety system. It provides the CPython interpreter, which can be invoked in several ways.

There are some small samples and scripts for demos and testing. This demo exhibits many Piety features.

Other pages describe the Piety directories and their contents, and its modular structure.

NOTE: The preceding paragraphs describe the Piety version in the master branch, labelled with the version1 tag. Work on this version ended in Jan 2023. A total rewrite is now underway in the rewrite branch to simplify the code and improve its organization and clarity. It might be quite a while before the code in rewrite provides equivalent functionality to master.

This project is a series of experiments. There is no plan for a sequence of steps to bring Piety to some completed, finished state. Instead, here are some notes about my working method, and some experiments I might try in the future.

I have brought Piety to its present state by working in short bursts on an irregular schedule, when I can find the time and interest. I decide what to work on next as I go along. I often go back and rewrite what I have already done, to make it easier to work with or just to improve the style.

A history of some of this past work appears here (it omits the early years).

I hope someday to run Piety on a bare machine with no other operating system, but only a Python interpreter with minimal support.

Piety divides naturally into two independent parts: the hosted part and the native part. The hosted part can run in any Python interpreter. It includes the applications, shells, job control, tasking, and the programming environment. The native part includes the Python interpreter itself, and the support needed to run the interpreter on the computer hardware. Almost any general-purpose operating system can serve as the support, but the goal is to replace that with a special-purpose operating system which is itself mostly written in Python.

All the work I have done so far, including the programming environment, is in the hosted part. I have researched several approaches to building the native part, but have not begun work on any. Every approach would require a more concentrated, sustained effort than I have been able to make so far.

It is likely that work in the near future will continue in the hosted part. I can always add features and improve the convenience of the programming environment. I might add other hosted applications, for example a simple text-only web browser in pure Python.

At this stage, the experiment is to see if it can be possible to create, edit, and run Python code using only the programming environment we have built so far, without resorting to the host desktop or command line.

I will try to observe the discipline that Piety is self-hosted: any new Piety code must be developed within its already existing programming environment.

NOTE: At this writing (Feb 2023) a total rewrite is underway in the rewrite branch to simplify the code and improve its organization and clarity.

The Piety system has no dependencies, other than Python itself (including a few standard library modules). This makes Piety a minimal self-contained system, written in a uniform style throughout. Alternatively, it might be possible to assemble similar functionality from other projects, but I expect the resulting system would be larger and harder to understand than Piety.

Piety is written in Python 3 since June 2015. Earlier work is saved in this repository in the python2 tag. The conversion is described here. Piety now requires Python 3.5.

The Piety software has only run on one computer: a MacBook Pro (13 inch, early 2011), running Mac OS (through 10.11.6 El Capitan, the most recent version that runs on that hardware). It has only run in the Mac OS Terminal, through version 2.6.2 (361.2). It has only run on CPython downloaded from python.org, through version 3.9.0.

Revised Feb 2023