envstamp

Atomic, reproducible fingerprints of installed Python distributions.

envstamp is a small stdlib-only package for recording installed package versions and content fingerprints in an atomic JSON stamp.

Installation

pip install envstamp

envstamp requires Python 3.12 or newer.

CLI

Get a stamp for one or more installed distributions and print it:

envstamp get numpy pandas

Atomically write the stamp to a file:

envstamp get numpy pandas --output /tmp/envstamp.json

Read the saved stamp:

envstamp read /tmp/envstamp.json

Each package record contains its canonical name, installed version, fingerprint algorithm, package-level SHA-256, and the number of files included in that digest. Package records are sorted by canonical name.

Python API

from envstamp.stamp import get_stamp, read_stamp, write_stamp


stamp = get_stamp(["numpy", "pandas"])
write_stamp("/tmp/envstamp.json", stamp)

saved = read_stamp("/tmp/envstamp.json")
for package in saved.packages:
    print(package.name, package.version, package.sha256)

envstamp supports regular, non-editable installations. It reads .dist-info/direct_url.json when present and rejects the distribution when dir_info.editable is true, because that metadata points at a mutable source tree rather than a stable installed payload.

Fingerprint protocol

The envstamp-sha256-v1 algorithm starts from each installed distribution manifest, but only includes entries that resolve inside its installation root, normally site-packages. This covers Python code, native libraries such as .so and .pyd, and package data. Distribution metadata, bytecode caches, .pth and .egg-link path files, launch scripts, and external data are excluded.

RECORD hashes are not used as an inclusion filter. When an included entry has no RECORD hash, envstamp still reads and hashes the installed file directly. If that file is missing, fingerprinting fails instead of silently producing a partial digest.

File paths are sorted before the package digest hashes the protocol tag followed by path\0sha256\0size\n records. The read buffer size does not affect the resulting digest.

Atomic writes

Each stamp file belongs to one writer and contains one complete stamp. A write creates a same-directory temporary file, flushes it, and atomically replaces the previous stamp file. On POSIX, readers therefore observe either the previous complete stamp or the new complete stamp. Concurrent writers to the same path are not supported; use a separate file for each process.