clued 0.1.1

Ergonomic error context for Python exceptions, built on PEP 678 add_note()

Clued

Leave clues for your future debugging self.

clued attaches structured, human-readable context to exceptions as they propagate — without changing the exception type, wrapping in a new exception, or parsing strings later.

Install

Install with pip

pip install clued

or install with uv

uv add clued

Requires Python 3.11+. Zero dependencies.

The Problem

When an error happens deep in your call stack, you typically get one of two outcomes:

Option A — bare exception, no context:

def process_order(order_id):
    user = get_user(order_id)   # raises ValueError("invalid id format")
    charge(user)

ValueError: invalid id format
  File "app.py", line 2, in get_user

The traceback tells you where it happened, not why. You don't know which order, which user, or what the system was trying to do at a higher level.

Option B — verbose try/except wrapping:

def process_order(order_id):
    try:
        user = get_user(order_id)
    except ValueError as e:
        raise OrderProcessingError(
            f"failed to process order {order_id}: could not fetch user"
        ) from e

This works, but it's tedious. Every layer of your call stack needs its own try/except/raise from block. Real codebases end up with dozens of custom exception classes and repetitive wrapping code. Most developers just don't bother — and then they're debugging production issues with a KeyError: 'name' and no idea which record or request caused it.

With clued:

from clued import clue

def process_order(order_id: str, user_id: int) -> None:
    with clue("processing order", order_id=order_id, user_id=user_id) as ctx:
        ctx.refine(step="fetch user")
        user = get_user(order_id)

        ctx.refine(step="charge")
        charge(user)

ValueError: invalid id format
  File "app.py", line 4, in get_user
- Clue 0: processing order [order_id='BAD', user_id=-1, step='fetch user'] (app.py:8)

Clues nest naturally across call boundaries — each layer adds its own note, inner-to-outer:

from clued import clue

def process_order(order_id: str, user_id: int) -> None:
    with clue("processing order", order_id=order_id, user_id=user_id):
        charge_user(order_id, user_id)

def charge_user(order_id: str, user_id: int) -> None:
    with clue("charging user", user_id=user_id) as ctx:
        ctx.refine(step="fetch card")
        card = get_card(user_id)

        ctx.refine(step="apply charge")
        apply_charge(card, order_id)

ValueError: invalid card format
  File "app.py", line 4, in get_card
- Clue 0: charging user [user_id=-1, step='fetch card'] (app.py:11)
- Clue 1: processing order [order_id='BAD', user_id=-1] (app.py:5)

One with block. No custom exception class. No raise from. The context travels with the exception automatically.

Quick Start

from clued import clue, get_clues

with clue("loading config", path=path, env=env) as ctx:
    ctx.refine(section="database")
    load_db_config(path)

On any exception raised inside the block, clued calls add_note() (PEP 678) to attach a formatted string, and stores a structured ClueRecord you can query in code:

except Exception as e:
    for record in get_clues(e):
        print(record.msg, dict(record.kv), f"{record.filename}:{record.lineno}")

Nested with clue(...) blocks each add their own note — outermost last, so the traceback reads inner-to-outer.

Features

• Structured kv — context stored as typed key-value pairs, not just strings
• Source location — note includes the exact file and line where clue() or refine() was called
• refine() — narrow context in-place as a block progresses (e.g. track loop index, current step)
• Async-safe — uses ContextVar for per-task isolation; works with asyncio.gather and thread pools
• Zero dependencies — stdlib only
• Fully typed — ships a py.typed marker, passes mypy strict and pyright

API Reference

Symbol	Description
clue(msg, **kv)	Context manager. Attaches context on any exception raised within the block. Yields a ClueHandle.
ClueHandle.refine(msg=None, **kv)	Update context in-place. None values delete a key.
ClueHandle.reset()	Restore to original message and clear all kv.
clue_on_error(msg_template, **kv)	Decorator. Formats msg_template with bound arguments and wraps the call in clue(). Works on async functions too.
ctx(fn, *args, msg, **kv)	Inline wrapper. Calls fn(*args) inside a clue() context.
get_clues(exc)	Returns list[ClueRecord] attached to the exception.
get_clue_dict(exc)	Returns a flat merged dict of all kv (inner clues override outer).
current_clues()	Returns the active tuple[ClueHandle, ...] stack for the current context (useful for logging).

ClueRecord

@dataclass(frozen=True)
class ClueRecord:
    msg: str
    kv: frozenset[tuple[str, Any]]
    filename: str
    lineno: int

Usage Patterns

Decorator

from clued import clue_on_error, clue_on_error_async

@clue_on_error("processing item {item_id}", source="worker")
def process_item(item_id: str) -> None:
    ...

@clue_on_error_async("fetch user {user_id}")
async def fetch_user(user_id: int) -> dict[str, str]:
    ...

Inline wrapper

from clued import ctx

result = ctx(load_file, path, msg="loading file", path=path)

Tracking progress in a loop

with clue("batch processing", total=len(items)) as ctx:
    for i, item in enumerate(items):
        ctx.refine(index=i, item_id=item["id"])
        process_item(item)

If the batch fails at item 42, the exception note shows exactly which item and index.

Logging integration

import logging
from clued import current_clues

class ClueFilter(logging.Filter):
    def filter(self, record):
        for handle in current_clues():
            record.__dict__.update(handle.kv)
        return True

How It Works

clued is built on two Python stdlib primitives:

• PEP 678 add_note() (Python 3.11+) — the standard way to attach strings to exceptions. Tools like pytest, rich, and IPython already render __notes__, so you get readable output for free.
• contextvars.ContextVar — each asyncio task and thread inherits a copy-on-write context, so nested tasks each carry their own clue stack and cannot interfere with each other.

When an exception exits a clue block, two things happen:

1. A formatted string (- Clue N: msg [k=v] (file:line)) is appended via add_note(), where N is the depth index (0 = innermost).
2. A ClueRecord is appended to exc.__clues__ for structured access.

No monkeypatching. No custom exception base class. No runtime overhead on the happy path.

Development

# Set up or Sync python environment
make sync

# Ruff formatter
make fmt

# Ruff linter & Mypy static type check
make check

# Pytest
make test

License

MIT