Re:MCP Run Python
by singularity2001 on Thursday April 17, 2025 @03:38PM
(#43721214)
one wasmtime dependency and a self contained python file with 100 loc seems reasonable!
much better than calling deno, at least if you have no pip dependencies...
just had to update to new api:
# store.add_fuel(fuel) store.set_fuel(fuel) fuel_consumed=fuel-store.get_fuel()
and it works!!
time to hello world: hello_wasm_python311.py 0.20s user 0.03s system 97% cpu 0.234 total
it's pretty difficult to package native python dependencies for wasmtime or other wasi runtimes, e.g. lxml
Re:MCP Run Python
by Already__Taken on Friday April 18, 2025 @07:02AM
(#43726861)
yeh if you can't shove numpy in there its not really useful.
I was interested in how this compares in a kind of absolute sense. For comparison, an optimized C hello world program gave these results using `perf` on my Dell XPS 13 laptop:
0.000636230 seconds time elapsed
0.000759000 seconds user
0.000000000 seconds sys
(Yes I used percentages to underscore how big the difference is. It's 368x and 209x respectively. That's huge.)
Begrudgingly, here are the standard Python numbers:
real 0m0.019s
user 0m0.015s
sys 0m0.004s
Re:MCP Run Python
by singularity2001 on Thursday April 17, 2025 @08:00PM
(#43723565)
haha, 99% is startup time for the sandbox, but yeah, python via wasm is probably still 10-400 times slower than c.
Great, thanks for your post! I got it working too. This is going to be incredibly handy.
https://github.com/abshkbh/arrakis
Will come with MacOS support very soon :) Does work on Linux
I tried this path and found that MacOS has horrible support on firecracker and similar.
Crosvm (our original Google project) and its children projects Firecracker, Cloud-Hypervisor are all based on top of "/dev/kvm" i.e. the Linux Virtualization stack.
Apple's equivalent is the Apple Virtualization Framework which exposes kvm like functionality at a higher level.
Atleast on macos cant the sandbox-exec be used similar to what codex is doing?
Yeah, I got excited about that option a while back but was put off by the fact that Apple's (minimal) documentation say sandbox-exec is deprecated.
OpenAI's Codex CLI uses it on macOS. It's in typescript but maybe I'll take a look at what they do and port it to python.
I cleaned up the output of asking Gemini 2.5 Pro to rewrite it in python, and it seems to work well:
https://gist.github.com/fzzzy/319d6cbbdfff9c340d0e9c362247ae...
> I'm hoping some day to find a recipe I really like for running Python code in a WASM container directly inside Python.
But what would be the usecase for this?
Running Python code from untrusted sources, including code written by LLMs.
I see, the way I would approach is it by running a client on in a specific python env on an incus instance, with LLM hosted either on the host or another seperate an incus instance. Lately been addicted to sandboxing apps in incus, specifically for isolated vpn tunnels, and automating certain web access.
The demo looks really appealing. I have a real-world use case in mind: analyzing an Excel file and asking questions about its contents. The current approach (https://github.com/pydantic/pydantic-ai/blob/main/mcp-run-py...) seems limited to running standalone scripts—it doesn't support reading and processing files. Is there an extension or workaround to enable file input and processing?
I'm hoping some day to find a recipe I really like for running Python code in a WASM container directly inside Python. Here's the closest I've got, using wasmtime: https://til.simonwillison.net/webassembly/python-in-a-wasm-s...