errortools 2.3.0

errortools - a toolset for working with Python exceptions and warnings and logging.

errortools

A lightweight Python exception handling utility library.

Features

• Raise Exceptions: raises(), raises_all(), reraise() — batch raising and exception conversion
• Catch & Suppress: ignore(), ignore_subclass(), ignore_warns(), fast_ignore(), super_fast_ignore(), timeout(), retry() — graceful suppression of exceptions and warnings, with automatic retry
• Exception Caching: error_cache — cache exceptions raised by functions (similar to lru_cache)
• Custom Exceptions: PureBaseException, ContextException, BaseErrorCodes, BaseWarning — structured exception classes with error codes, trace IDs, and context
• Attribute Error Mixin: Customize error behavior for attribute access, assignment, and deletion
• Type Aliases: ExceptionType, AnyErrorCode, BaseErrorCodesType, and more
• Logging: logger — loguru-inspired structured logger with leveled output, multiple sinks, context binding, and exception capture

Installation

pip install errortools

---

Examples

import warnings
from errortools import (
    ignore, fast_ignore, ignore_subclass, ignore_warns, timeout, retry,
    reraise, raises, raises_all, assert_raises,
    error_cache,
    PureBaseException, ContextException, BaseErrorCodes, BaseWarning,
)
from errortools.future import super_fast_ignore

# ── 1. ignore ── context manager with full metadata ──────────────────────────
with ignore(KeyError) as err:
    _ = {}["missing"]

assert err.be_ignore          # True  — was suppressed
assert err.name == "KeyError" # exception class name
assert err.count == 1         # how many times suppressed
assert err.exception          # the original KeyError instance
assert err.traceback          # full formatted traceback string

Attributes on the returned object:

Attribute	Type	Description
be_ignore	bool	True if an exception was suppressed
name	str | None	Class name of the suppressed exception
count	int	Number of suppressed exceptions
exception	Exception | None	The original exception instance
traceback	str | None	Formatted traceback string for debugging

Examples

# ── ignore as a decorator ──
@ignore(ValueError, TypeError)
def parse(x: str) -> int:
    return int(x)

parse("bad")  # suppressed → returns None

# ── 2. fast_ignore / super_fast_ignore ── zero-overhead hot-path suppression ─
with fast_ignore(KeyError, IndexError):
    _ = [][0]                 # suppressed, no metadata collected

with super_fast_ignore(KeyError):
    _ = {}["x"]              # absolute minimal overhead

# ── 3. ignore_subclass ── suppress any subclass of a base ────────────────────
with ignore_subclass(LookupError):
    raise IndexError("out of range")   # IndexError ⊆ LookupError — suppressed

# ── 4. ignore_warns ── silence warnings ──────────────────────────────────────
with ignore_warns(DeprecationWarning):
    warnings.warn("old api", DeprecationWarning)   # no output

with ignore_warns():           # suppress everything
    warnings.warn("anything")

# ── 5. timeout ── cancel async functions that take too long ──────────────────
@timeout(5.0)
async def fetch_data(url: str) -> bytes:
    ...                               # any async operation

# asyncio.TimeoutError raised automatically if it exceeds 5 s

# ── 6. retry ── automatically retry on failure ───────────────────────────────
@retry(times=3, on=ConnectionError, delay=1.0)
def connect(host: str) -> None:
    ...                               # retried up to 3 times on ConnectionError

# works with async functions too
@retry(times=5, on=TimeoutError, delay=0.5)
async def fetch(url: str) -> bytes:
    ...

# multiple exception types
@retry(times=2, on=(ValueError, KeyError))
def parse(data: dict) -> str:
    return data["key"]

# ── 7. reraise ── convert exception types on the fly ─────────────────────────
with reraise(KeyError, ValueError):
    raise KeyError("missing key")      # → ValueError: 'missing key'

with reraise((KeyError, IndexError), RuntimeError):
    _ = [][99]                         # → RuntimeError: list index out of range

# ── 8. raises / raises_all ── batch raise ────────────────────────────────────
raises([ValueError], ["bad input"])    # → ValueError: bad input

raises_all(
    [ValueError, TypeError],
    ["bad input"],
)                                      # → ExceptionGroup (2 sub-exceptions)

# ── 9. assert_raises ── assert a callable raises ─────────────────────────────
exc = assert_raises(int, [ValueError], "not-a-number")
print(exc)   # invalid literal for int() with base 10: 'not-a-number'

# ── 10. error_cache ── cache exceptions by call arguments ─────────────────────
@error_cache(maxsize=64)
def load(user_id: int) -> dict:
    if user_id < 0:
        raise ValueError(f"invalid id: {user_id}")
    return {"id": user_id}

with ignore(ValueError):
    load(-1)              # raises, exception cached for args (-1,)

print(load.cache_info())  # CacheInfo(hits=0, misses=1, maxsize=64, currsize=1)
load.clear_cache()

# ── 11. Custom exceptions — three layers ──────────────────────────────────────

# Layer 1: PureBaseException — code + detail only
class AppError(PureBaseException):
    code = 9000
    default_detail = "Application error."

print(AppError())         # [9000] Application error.
print(repr(AppError()))   # AppError(detail='Application error.', code=9000)

# Layer 2: ContextException — adds trace_id, context dict, exception chaining
class ServiceError(ContextException):
    code = 9001
    default_detail = "Service unavailable."

try:
    raise ConnectionError("db timeout")
except ConnectionError as cause:
    err = (
        ServiceError("downstream failed")
        .with_context(service="postgres", retries=3)
        .with_cause(cause)
    )
    print(err.trace_id)    # 'a3f1c8...' — unique per instance
    print(err.context)     # {'service': 'postgres', 'retries': 3}
    print(err.chain)       # [{'type': 'ServiceError', 'code': 9001, ...}]
    print(err.traceback)   # compact stack trace joined by |

# Layer 3: BaseErrorCodes — predefined factory methods
raise BaseErrorCodes.invalid_input("username too short")  # InvalidInputError  [1001]
raise BaseErrorCodes.access_denied()                      # AccessDeniedError  [2001]
raise BaseErrorCodes.not_found("user #42")                # NotFoundError      [3001]
raise BaseErrorCodes.runtime_failure("crash")             # RuntimeFailure     [4001]
raise BaseErrorCodes.timeout_failure()                    # TimeoutFailure     [4002]
raise BaseErrorCodes.configuration_error("missing key")   # ConfigurationError [5001]

# ── 12. BaseWarning ── structured warnings with factory methods ───────────────
class ExperimentalWarning(BaseWarning):
    default_detail = "This feature is experimental."

ExperimentalWarning.emit()                          # uses default_detail
ExperimentalWarning.emit("use at your own risk")    # custom message

BaseWarning.deprecated("use new_api() instead").emit()   # DeprecatedWarning
BaseWarning.performance("O(n²) detected").emit()         # PerformanceWarning
BaseWarning.resource("file handle leak").emit()          # ResourceUsageWarning

---

Logging

errortools.logging is a loguru-inspired structured logger with no external dependencies.

Quick start

from errortools.logging import logger

logger.info("Server started on port {}", 8080)
logger.warning("Disk at {pct:.1f}%", pct=92.5)
logger.success("All systems operational")

Output (colourised in a terminal):

2026-01-01 12:00:00.123 | INFO     | app:main:42 - Server started on port 8080
2026-01-01 12:00:00.124 | WARNING  | app:main:43 - Disk at 92.5%
2026-01-01 12:00:00.125 | SUCCESS  | app:main:44 - All systems operational

Log levels

Method	Level	No
logger.trace()	TRACE	5
logger.debug()	DEBUG	10
logger.info()	INFO	20
logger.success()	SUCCESS	25
logger.warning()	WARNING	30
logger.error()	ERROR	40
logger.critical()	CRITICAL	50

Sinks

Add and remove destinations at runtime. Each sink has its own level filter.

from errortools.logging import logger, Level

# stream (stderr by default, auto-detects TTY colour)
logger.add(sys.stdout, level="WARNING")

# file with rotation (bytes) and retention (number of old files to keep)
sid = logger.add("logs/app.log", rotation=10_485_760, retention=5)

# any callable
logger.add(print)

# remove by id, or pass no argument to remove all
logger.remove(sid)
logger.remove()

Level filtering

logger.set_level("WARNING")   # or Level.WARNING or numeric 30
logger.debug("dropped")       # below threshold — not emitted
logger.warning("kept")        # at threshold — emitted

Context binding

bind() returns a new logger that carries extra fields in every record. The original logger is unmodified.

req_log = logger.bind(request_id="abc-123", user="alice")
req_log.info("Request received")   # record.extra contains request_id and user

# Stacking
db_log = req_log.bind(db="postgres")
db_log.debug("Query OK")           # extra: request_id, user, db

Exception capture

# Attach the current traceback to any log call
try:
    connect()
except ConnectionError:
    logger.exception("DB connection failed")       # logs at ERROR + traceback

# Equivalent long-hand
logger.opt(exception=True).error("DB connection failed")

catch() — auto-log and suppress

# As a context manager
with logger.catch():
    int("not a number")   # logged at ERROR, then suppressed

# Re-raise after logging
with logger.catch(ConnectionError, reraise=True):
    connect()

# As a decorator
@logger.catch(ValueError)
def parse(s: str) -> int:
    return int(s)

Custom format string

logger.add(
    "debug.log",
    fmt="{time} | {level} | {name}:{function}:{line} - {message}",
)

Available placeholders: {time}, {level}, {name}, {file}, {line}, {function}, {message}.