Reference library

Errors & debugging

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

4 matches

How to Assert Preconditions with Descriptive Messages in Python

Use Python's assert statement with a custom message to validate function preconditions and fail fast with clear diagnostics.

assert debugging preconditions

Python

def divide(dividend, divisor):
    assert divisor != 0, f"Divisor must be non-zero, got {divisor!r}"
    return dividend / divisor


if __name__ == "__main__":
    print(divide(10, 2))
    try:
        divide(10, 0)
    except AssertionError as e:
        print(f"AssertionError: {e}")

15 0 Open

Errors & debugging easy

How to Record Last N Errors with a Ring Buffer in Python

Use collections.deque with maxlen to keep only the most recent N error messages while discarding older entries automatically.

ring-buffer deque error-handling

Python

import collections

class ErrorRecorder:
    def __init__(self, size):
        self.buffer = collections.deque(maxlen=size)

    def record_error(self, message):
        self.buffer.append(message)

    def get_errors(self):
        return list(self.buffer)

if __name__ == "__main__":
    recorder = ErrorRecorder(3)
 …

13 0 Open

Errors & debugging easy

How to Serialize an Exception to a JSON-Safe Dict in Python

Convert any Python exception into a JSON-safe dictionary with type, message, and the last few traceback lines for logging.

exceptions json logging

Python

import json
import traceback
from typing import Any


def exception_to_dict(exc: Exception) -> dict[str, Any]:
    """Convert an exception into a JSON-safe dictionary."""
    return {
        "type": type(exc).__name__,
        "message": str(exc),
        "traceback": traceback.format_exc().strip().split("\n")[-3:],
…

15 0 Open

Errors & debugging medium

How to parse a traceback to get the last frame in Python

Extracts the innermost frame's file, line, and function name from a Python traceback object.

traceback exceptions debugging

Python

import sys
import traceback


def parse_traceback_last_frame(exc_info):
    """Return the file, line, and function of the last (innermost) frame."""
    _, _, tb = exc_info
    last_tb = tb
    while last_tb.tb_next is not None:
        last_tb = last_tb.tb_next
    filename = last_tb.tb_frame.f_code.co_filename
    l…

13 0 Open

Browse by section

Each section groups closely related Python snippets.