Handit Core (Python)

Lightweight function and HTTP tracing for Python applications with zero configuration. Captures function calls/returns with arguments and return values, and outgoing HTTP requests/responses (including bodies) for requests and httpx. Events are buffered in-memory and written once at process exit to handit_events.jsonl.

Install

Build from source (requires Rust and Python toolchain):

python -m pip install maturin
python -m maturin develop --release -m python/pyproject.toml

Quick start

from handit import session, tracing
import requests

@tracing(agent="demo")
def fetch_user(user_id: int) -> dict:
    resp = requests.get(f"https://httpbin.org/anything/{user_id}")
    return resp.json()

if __name__ == "__main__":
    with session(tag="demo-session"):
        fetch_user(42)
# Events will be written to ./handit_events.jsonl at exit

What is captured

• Function events: call/return/exception
  • Arguments preview on call
  • Return value preview on return
• HTTP events (client-side)
  • requests/httpx: method, URL, headers, request body; response status, headers, body, size, duration, error
  • aiohttp: method, URL, headers; response status, headers (bodies are not captured by default)

Behavior

• Zero-config: HTTP instrumentation is enabled on import; no environment variables are required.
• Noise reduction: internal library frames and stdlib/site-packages are excluded by default.
• Output: events are buffered and flushed once at exit to handit_events.jsonl.
  • Override path via env HANDIT_OUTPUT_FILE=./path/file.jsonl.

Advanced

• Manual flush during runtime:

from handit_core import handit_core_native as native
native.flush_events_to_file("./handit_events.jsonl")

• Optional envs (all have safe defaults):
  • HANDIT_INCLUDE / HANDIT_EXCLUDE: module/function regex filters
  • HANDIT_MAX_STR (default 256), HANDIT_MAX_LOCALS (default 64)
  • HANDIT_REDACT: regex for keys to redact in previews
  • HANDIT_CAPTURE_ONLY_CWD (default true)

Notes

• Capturing full HTTP bodies may include sensitive data. Ensure you comply with your data policy.
• For aiohttp streamed bodies, body capture can be added with explicit buffering middleware if needed.