codehound

An AST-based static analyzer that hunts real bugs in large Python codebases — seven of the ten rules are backed by a bug that was actually found and merged into a major open-source AI framework; the other three are hardening rules verified against real false positives instead.

Most linters flag style. codehound flags the subtle correctness and async-safety bugs that slip past code review and only bite in production — event-loop stalls, shared mutable state, leaked file descriptors, fire-and-forget tasks that get garbage-collected mid-run.

Each of the six checks below isn't theoretical. I wrote it after finding — and fixing, via a merged pull request — that exact bug in a real, popular framework (agno 25k⭐, crewAI 30k⭐, mem0, huggingface_hub).

See it in action

Pointing codehound at agno (a 25k⭐ AI agent framework) surfaced real, previously-unreported bugs:

$ codehound scan agno/libs/agno/agno --select CH001,CH006

agno/integrations/discord/client.py:90:26: CH001 `requests.get()` blocks the event loop
    inside async function `on_message`; use the async equivalent.
agno/tracing/exporter.py:112:16: CH006 `asyncio.create_task(...)` result is discarded;
    keep a reference (the loop only holds a weak ref, so the task may be GC'd mid-run).

Found 2 issue(s) (CH001: 1, CH006: 1)

Both of these became merged/​open fixes upstream. The first froze the Discord bot's event loop on every video/document attachment; the second could silently drop telemetry when its export task was garbage-collected mid-run. codehound found them in seconds — see docs/FINDINGS.md for the full provenance of every rule.

Why this exists

I was contributing bug fixes to large AI frameworks and noticed the same handful of mistakes recurring across codebases. Instead of hunting them by hand, I encoded each one as an AST rule. codehound is the result: point it at a repo and it finds the bugs I'd otherwise have to read 100k lines to spot.

It found the bugs behind these merged fixes — and is built to find the next one.

Install

pip install codehound

Zero dependencies — it's ~750 lines on top of the standard-library ast module, so this installs instantly and runs fully offline, no API key or network call involved.

pip install -e .

# or run straight from source, no install needed
PYTHONPATH=src python -m codehound.cli scan path/to/project

Usage

# scan a project (skips tests/, docs/, examples/, vendored code by default)
codehound scan path/to/project

# only run specific checks
codehound scan path/to/project --select CH001,CH006

# machine-readable output for CI dashboards
codehound scan path/to/project --format json
codehound scan path/to/project --format csv

# list every available check
codehound list

codehound scan exits non-zero when it finds issues, so it drops straight into CI:

- run: codehound scan src   # fails the build on a regression

The checks

codehound list prints this from the source of truth.

CH007-CH010 don't have found-and-merged bugs behind all of them the way CH001-CH006 do - three are hardening rules for well-known Python correctness gotchas rather than something this project personally tracked down first. CH010 is the exception: it found a genuine, serious bug on its own, in HuggingFace's accelerate - see below. Building all four surfaced real false positives, each one fixed before shipping:

• CH007 (agno): a bare self.foo() call matched against an unrelated same-named async def foo on a different class (agno's own sync/async "twin method" convention, e.g. ZepTools/ZepAsyncTools), and a plain callable parameter shadowed by an unrelated same-named async function hundreds of lines away in the same file.
• CH009 (llama_index): a thread handed off through a different object's attribute, not self - chat_response.write_response_to_history_thread = thread, with chat_response itself returned and the thread joined later once the caller finishes consuming the stream.
• CH010 (marimo): sorted(rows, key=lambda row: row[sort_arg.by]) inside for sort_arg in ... - the lambda references the loop variable, but sorted() calls it immediately, synchronously, before the next iteration moves sort_arg on. Nothing outlives the iteration. This reshaped the check entirely: it now only fires when a lambda is directly stored (.append(...), assignment, return), not merely passed as a callback argument to something that consumes it on the spot.

The accelerate find (CH010): MegatronEngine.get_module_config builds one callback per model chunk for distributed-training parameter sync: [lambda x: self.optimizer.finish_param_sync(model_index, x) for model_index in range(len(self.module))]. Every lambda captures model_index by reference; by the time any of them actually runs, the comprehension has finished and model_index holds its final value for all of them - whichever chunk's callback fires, it reports the last chunk's index. Fixed with the standard default-argument capture (model_index=model_index) and a regression test that fails on the pre-fix code (all three callbacks report index 2) and passes on the fix. PR: huggingface/accelerate#4273.

Scanning ~20 major Python AI/ML frameworks with the fixed CH007/CH008/CH009 turned up zero further real instances beyond the ones above - itself a result, not a null: CH008's bug fails immediately and unconditionally, so it's very unlikely to survive basic testing; CH007 and CH009 both only match same-file names by design, and most real cases of either are plausibly cross-module.

One check we built and did not ship: CH011 exception-chaining (except X as e: raise Y(...) with no from e, discarding the real traceback - overlaps flake8-bugbear B904). It worked exactly as designed, but at a scale that says more about how common the pattern is than about anything worth flagging: 1,911 hits across the same ~20-framework corpus. Shipping a check that fires that often would make every scan result mostly CH011 noise, undermining the "a finding must be defensible" standard the rest of this tool holds itself to. Built, measured, and deliberately left out - a real decision, not an oversight.

How it works

codehound/
├── core.py          # file discovery, AST parsing, the Finding/Check contract,
│                    #   and a child→parent map so checks can ask "what's my
│                    #   enclosing function / am I inside a `with`?"
├── cli.py           # `scan` / `list`, text|json|csv output, CI-friendly exit codes
└── checks/          # one small, independently-tested class per rule
    ├── blocking_async.py     (CH001)
    ├── mutable_defaults.py   (CH002)
    ├── datetime_utcnow.py    (CH003)
    ├── get_event_loop.py     (CH004)
    ├── resource_leak.py      (CH005)
    ├── floating_task.py      (CH006)
    ├── unawaited_coroutine.py (CH007)
    ├── asyncio_run_in_loop.py (CH008)
    ├── floating_thread.py     (CH009)
    └── loop_closure_capture.py (CH010)

Each check receives a parsed ast tree plus the precomputed parent map and returns Findings. Adding a rule is one file + one registry line + a test. See docs/ARCHITECTURE.md for a full walkthrough of the engine, the parent map, and the design decisions.

False-positive discipline is a feature. CH005 won't flag a handle that's returned (the caller owns it) or explicitly .close()d. CH006 won't flag TaskGroup.create_task (the group holds the reference). CH001 only fires when the enclosing function is async. CH007 scopes self.foo() matches to async methods on the same class as the call site, and bare foo() matches to module-level async functions that aren't shadowed by a same-named parameter. CH009 doesn't flag a thread handed off as any object's attribute, not just self. CH010 only fires when a lambda is directly stored (appended, assigned, returned), not merely passed as a callback argument that gets consumed on the spot. All four of those guards exist because of real false positives caught while building the checks (see above). The test suite asserts both "bad code is flagged" and "correct code is not."

Tests

pip install -e ".[dev]"
pytest -q

Every check has paired tests: the buggy pattern is flagged, and the idiomatic fix is not.

Roadmap

• await on a non-awaited coroutine (missing-await detection) — CH007
• PyPI release — pip install codehound
• asyncio.run() inside a running loop — CH008
• Non-daemon thread started without a join — CH009 (the thread analog of CH006)
• Loop-variable closure capture in lambdas — CH010
• Cross-module resolution for CH007/CH009 (currently same-file only)
• Sync HTTP clients constructed inside async request handlers
• --fix for the mechanical rules (CH002, CH003, CH004)
• Pre-commit hook

License

MIT © Abhinav Tarigoppula