Guido uploaded this to alt.sources on February 20, 1991. It predates classes (those came in 0.9.4), has no list.append, and only understands single-quoted strings. It is a fully working Python interpreter you can build and run today.

Here is how Guido described it at the time:

This is Python, an extensible interpreted programming language that combines remarkable power with very clear syntax.

Python can be used instead of shell, Awk or Perl scripts, to write prototypes of real applications, or as an extension language of large systems, you name it. There are built-in modules that interface to the operating system and to various window systems: X11, the Mac window system (you need STDWIN for these two), and Silicon Graphics' GL library. It runs on most modern versions of UNIX, on the Mac, and I wouldn't be surprised if it ran on MS-DOS unchanged.

Building and installing Python is easy (but do read the Makefile). A UNIX style manual page and extensive documentation (in LaTeX format) are provided.

— Guido van Rossum, CWI Amsterdam, 1991

Build

macOS

cd src
make python
./python

Requires Xcode Command Line Tools (xcode-select --install). Tested on macOS 15 with Apple clang 17.

Linux (Docker / Podman)

docker build -t python091 .
docker run --rm -it python091

Tested on Debian bookworm inside Podman on macOS. Swap docker for podman if that is what you have.

Run

>>> print 'hello, 1991'
hello, 1991
>>> 1 + 1
2
>>> def fact(n): return 1 if n <= 1 else n * fact(n-1)

What works, what doesn't

The interpreter itself is solid. The demo scripts are a mixed bag:

The overflow bug: intobject.c checks for multiplication overflow using (long)0x80000000, which on a 64-bit system is +2147483648 instead of -2147483648. Every multiplication involving large constants triggers a false overflow. It is a known 32-bit assumption and not something we fixed.

See demo/README.md for full notes.

What changed from the original

Three minimal patches to compile on modern toolchains:

1. src/Makefile added -std=gnu89 -w -Wno-incompatible-function-pointer-types -DSIGTYPE=void to CFLAGS and dropped a hardcoded SGI path from DEFPYTHONPATH
2. src/ceval.h added a missing flushline() declaration (called in bltinmodule.c but never declared)
3. src/bltinmodule.c added #include "fgetsintr.h" (called fgets_intr() without the header)

Nothing in the language, bytecode, or standard library was touched. See Dockerfile for the Linux build recipe.

Docs

The original LaTeX documentation is in doc/. A readable Markdown version converted from all the .tex files is at doc/README.md.

There is also a Unix man page at python.man.

Original README

Guido's original note is preserved at README.old.

Thanks

Big thanks to Skip Montanaro for preserving and archiving the original source at smontanaro/python-0.9.1. Without that work this repo would not exist.

License

CWI 1991 open source license. See LICENSE.