LucidLog

LucidLog is a lightweight, source-aware exception diagnostic library for Python.

It keeps the original exception behavior intact, adds a clearer reading of the relevant traceback frame, and provides deterministic built-in explanations without requiring a remote service.

Quick start

import lucidlog

lucidlog.install()

try:
    value = {}["missing"]
except Exception:
    lucidlog.exception("Lookup failed")

Complete example

Run the bundled demo for a full tour of the library's features:

python examples/complete_demo.py

The demo covers chained exceptions, redaction, render output, custom rules, logging payloads, and the threading/asyncio integrations.

Public API

• lucidlog.install()
• lucidlog.uninstall()
• lucidlog.exception(message, *, stream=None, full=False, config=None)
• lucidlog.diagnose(exc, *, config=None)
• lucidlog.log_exception(logger, message, *, full=False, config=None)
• lucidlog.render_diagnostic(diagnostic, *, full=False, stream=None, color=None)

Configuration and output

Pass a frozen lucidlog.Config to install, diagnose, exception, or log_exception to configure capture and output:

import lucidlog
from lucidlog import Config

lucidlog.install(
    config=Config(
        color=True,
        include_full_traceback=True,
        max_chain_depth=6,
        redact_patterns=(r"(?i)customer-id=[A-Z0-9]+",),
    )
)

Colors are disabled for non-interactive streams by default and honor NO_COLOR and TERM=dumb. color=True forces ANSI output; color=False disables it. Exception colors distinguish common diagnostic families, while the severity badge uses a separate palette (critical, error, warning, or info). The JSON representation contains the plain text values, never ANSI codes.

Cause/context chains and exception groups are represented as bounded nested data and included in the compact output. Limits (max_chain_depth, max_group_exceptions, max_frames, max_message_length, max_traceback_chars, max_source_file_bytes, and max_diagnosis_evidence) constrain diagnostic capture. Diagnostic.to_dict() and to_json() include a schema version, severity, fingerprint-like ID, cause relationships, and truncation indicator. Setting include_local_variables=True or allow_network=True is rejected; those capabilities are deliberately not part of the core.

The optional runtime integrations are explicit:

from lucidlog.integrations.threading import install_threading_hook
from lucidlog.integrations.asyncio import install_asyncio_exception_handler

install_threading_hook()
install_asyncio_exception_handler()

Each has a corresponding uninstall_* function. Asyncio leaves an already-installed handler in place unless chain_previous=True; thread and main hooks restore prior handlers when removed. Worker-thread and event-loop hooks do not cover child processes.

Privacy notes

LucidLog never reads local variables or makes network requests. It redacts common credential-shaped strings and user-configured patterns from messages, source context, causes, and traceback text before those values enter the diagnostic model. Absolute paths under the home directory are shortened by default; root_path can shorten project paths. Redaction is best-effort: exception messages and source code are arbitrary application data, so review output before storing or forwarding it and supply additional patterns for your environment. Config validates regex syntax and output limits up front.

Logging integration writes one structured log record with a lucidlog dictionary in LogRecord extra fields. It deliberately omits exc_info to avoid bypassing redaction with a raw traceback. The original exception is not modified, and log_exception requires an active exception handler.

Tests

Run the unit and integration tests with:

python -m pytest

The suite covers chained and grouped exceptions, cycle/size limits, redaction, terminal colors, hook restoration, threading, asyncio, structured logging, and uncaught-process exit behavior.

Notes

• The core package is standard-library only.
• It does not capture local variables by default.
• It keeps the original traceback available and does not replace the application's original exception flow.