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Errors & debugging

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

5 matches

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.

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 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

Errors & debugging easy

How to define an exception hierarchy for domain errors in Python

Create a custom exception hierarchy with a base DomainError class and specific subclasses to handle validation, not-found, permission, and concurrency errors cleanly in Python apps.

exceptions domain-errors error-handling

Python

class DomainError(Exception):
    """Base class for all domain errors."""
    pass

class ValidationError(DomainError):
    """Raised when input data fails validation rules."""
    pass

class NotFoundError(DomainError):
    """Raised when a requested entity does not exist."""
    pass

class PermissionDeniedError(Dom…

14 0 Open

Errors & debugging easy

Implement a Context Manager That Suppresses Exceptions in Python

Shows how to write a custom context manager that catches specified exceptions and optionally re-raises others, plus the stdlib contextlib.suppress alternative.

context-manager exception-handling with-statement

Python

import contextlib

class SuppressExceptions:
    def __init__(self, *exceptions):
        self.exceptions = exceptions

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
        if exc_type is None:
            return False
        if not self.exceptions or exc_type in se…

11 0 Open

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