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Errors & debugging

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

6 matches

How to Handle ValueError with try except in Python

Shows a beginner-friendly try/except pattern that catches ValueError when converting text to an integer, prints a helpful message, and returns None instead of crashing.

try-except valueerror error-handling

Python

def parse_number(text):
    try:
        return int(text)
    except ValueError:
        print(f"ValueError: '{text}' is not a valid integer.")
        return None


if __name__ == "__main__":
    user_input = "abc"
    result = parse_number(user_input)
    print(f"Parsing '{user_input}' returned: {result}")

    vali…

15 0 Open

Errors & debugging easy

How to Return Success or Error as a Tuple in Python (Result Type Pattern)

Use a (bool, value) tuple as a lightweight Result type to return either a successful result or a descriptive error message from a Python function.

result type error handling tuple unpacking

Python

def divide(dividend: float, divisor: float) -> tuple[bool, float | str]:
    """Return (True, result) on success, (False, error_message) on failure."""
    if divisor == 0:
        return False, "Error: Division by zero"
    return True, dividend / divisor


if __name__ == "__main__":
    # Success case
    success, r…

11 0 Open

Errors & debugging easy

How to Test Exceptions in Python with pytest.raises

Learn the pytest.raises pattern to assert that specific exceptions are raised and validate their messages.

pytest testing exceptions

Python

import pytest


def divide(a: int, b: int) -> float:
    if b == 0:
        raise ValueError("Cannot divide by zero")
    return a / b


def test_divide_by_zero_raises():
    with pytest.raises(ValueError, match="Cannot divide by zero"):
        divide(10, 0)


def test_divide_by_zero_raises_exact_match():
    with py…

15 0 Open

Errors & debugging easy

How to Use Optional Return in Python Instead of Raising Exceptions

A Python function returns None for missing dictionary keys instead of raising KeyError, enabling graceful lookup handling with type hints.

optional typing dict-get

Python

from typing import Optional


def find_user(users: dict, user_id: int) -> Optional[dict]:
    """
    Look up a user by ID. Returns the user dict if found,
    otherwise returns None instead of raising KeyError.
    """
    return users.get(user_id)


def main() -> None:
    users = {
        1: {"name": "Alice", "ema…

15 0 Open

Errors & debugging easy

How to Validate an Email Address and Raise ValueError in Python

This code defines a validate_email function that checks an email address against a regex pattern and several rules, raising ValueError with a specific reason when invalid.

validation regex errors

Python

import re

def validate_email(email: str) -> str:
    """Validate an email address and return it if valid, otherwise raise ValueError."""
    if not isinstance(email, str):
        raise ValueError("Email must be a string")
    if len(email) > 254:
        raise ValueError("Email length exceeds 254 characters")

    #…

14 0 Open

Errors & debugging medium

Implement circuit breaker open after failures demo in Python

A minimal CircuitBreaker class that calls a function and automatically 'opens' after a set number of consecutive failures, blocking further calls with a RuntimeError.

circuit-breaker resilience error-handling

Python

import time
from datetime import datetime


class CircuitBreaker:
    def __init__(self, threshold=3):
        self.threshold = threshold
        self.failure_count = 0
        self.is_open = False

    def call(self, func, *args, **kwargs):
        if self.is_open:
            raise RuntimeError("Circuit is OPEN")
  …

13 0 Open

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