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Errors & debugging

Handle failures gracefully, raise helpful errors, and debug with confidence.

5 matches

How to Assert an Invariant After a Complex Transformation in Python

Use assert to verify that a multi-step transformation preserves a mathematical invariant, catching regressions early.

def transform_value(value):
    """Apply several transformations to a value."""
    doubled = value * 2
    shifted = doubled + 10
    normalized = shifted / 2
    return int(normalized)

def assert_invariant(value):
    """Assert that the transformation preserves a key invariant."""
    original = value
    transform…

13 0 Open

Errors & debugging easy

How to Log Exceptions with traceback.format_exc in Python

Capture and log a full traceback string when an exception occurs using Python's traceback.format_exc() and logging module.

traceback logging exception

Python

import traceback
import logging

def risky_operation(value):
    return 10 / value

logging.basicConfig(level=logging.ERROR, format='%(asctime)s - %(levelname)s - %(message)s')

def main():
    try:
        result = risky_operation(0)
        print(f"Result: {result}")
    except ZeroDivisionError:
        error_msg =…

14 0 Open

Errors & debugging easy

How to Raise a Custom Exception with Extra Context in Python

Define a custom exception that carries extra context fields and raise it to provide richer error information.

exceptions custom-exception error-handling

Python

class InsufficientFundsError(Exception):
    def __init__(self, balance, amount):
        self.balance = balance
        self.amount = amount
        super().__init__(f"Withdrawal of ${amount} failed: balance ${balance} is insufficient")


def withdraw(balance, amount):
    if amount > balance:
        raise Insuffici…

13 0 Open

Errors & debugging easy

Log to stderr with Python logging basicConfig

Configure Python's logging module to send all log messages to standard error (stderr) instead of the default stderr, with a readable timestamped format.

logging stderr debugging

Python

import logging

def main():
    logging.basicConfig(
        level=logging.DEBUG,
        format="%(asctime)s — %(name)s — %(levelname)s — %(message)s",
        stream=__import__("sys").stderr,
    )
    logger = logging.getLogger("example")
    logger.debug("Debug message")
    logger.info("Info message")
    logger.…

12 0 Open

Errors & debugging medium

Redact secrets from log message formatter in Python

Build a custom logging.Formatter that masks passwords, API keys, and credit card numbers in log output.

logging redaction security

Python

import re
import logging

class RedactingFormatter(logging.Formatter):
    """Formatter that masks sensitive data in log messages."""
    
    SENSITIVE_PATTERNS = [
        (re.compile(r'password[=:]\s*\S+', re.IGNORECASE), 'password=[REDACTED]'),
        (re.compile(r'api[_-]?key[=:]\s*\S+', re.IGNORECASE), 'api_key…

14 0 Open

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