Python

Summary

Item	Value
API name	python
source OCI image	python:3.12-alpine
per-job resource ceiling	1 vCPU, 512 MiB

The vCPU and RAM ceiling exists to prevent abuse; libkrun memory is elastic and the host only pays for what the guest touches.

Warmup

python3 -m compileall over the stdlib. The official image ships without .pyc files; compiling them into the image removes that cost from the first import. The image grew from 66 to 85 MiB and the warmup took ~1 s.

The warmup runs once, in the build VM, and the result is baked into the ext4. See Images.

How the code is executed

The main file (the first in files) is executed with python3 <file>. The other files sit in the same directory and can be imported. Everything runs in a directory under /tmp (tmpfs), in a fresh VM destroyed at the end of the job, with no network.

Building the image

rc image build --stack python

Example

curl -s http://127.0.0.1:8080/api/v1/run \
  -H 'Content-Type: application/json' \
  -d '{
    "language": "python",
    "files": [
      {"name": "main.py", "content": "from util import dobro\nprint(dobro(int(input())))\n"},
      {"name": "util.py", "content": "def dobro(x):\n    return 2 * x\n"}
    ],
    "stdin": "21"
  }'

Expected stdout: 42.

Measured numbers

On macOS 27.0.1, Apple Silicon: boot to the first response at p50 260 ms and p95 266 ms; a CLI job with a cold boot in ~240 ms total (execution 31–38 ms); through the API with a full pool, 26–43 ms. Image build: ~8–10 s. See Performance.