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Errors & debugging

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

5 matches

Collect Multiple Validation Errors in Python Before Raising

A chainable Validator class that accumulates all validation errors and raises them together in a single exception.

class ValidationError(Exception):
    pass

class Validator:
    def __init__(self):
        self.errors = []
    
    def validate_required(self, value, field_name):
        if not value:
            self.errors.append(f"{field_name} is required")
        return self
    
    def validate_email(self, email):
        …

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

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…

14 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 easy

How to check for None and raise helpful errors in Python

A defensive function that explicitly validates data, keys, and values — raising descriptive ValueError and KeyError exceptions before returning a result.

none error-handling validation

Python

def get_value(data, key):
    if data is None:
        raise ValueError("data cannot be None")
    if key not in data:
        raise KeyError(f"key '{key}' not found in data")
    result = data[key]
    if result is None:
        raise ValueError(f"value for key '{key}' is None")
    return result


if __name__ == "__…

15 0 Open

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