python-error-handlinglisted

# Python Error Handling Build robust Python applications with proper input validation, meaningful exceptions, and graceful failure handling. Good error handling makes debugging easier and systems more reliable. ## Core Concepts ### 1. Fail Fast Validate inputs early, before expensive operations. Report all validation errors at once when possible. ### 2. Meaningful Exceptions Use appropriate exception types with context. Messages should explain what failed, why, and how to fix it. ### 3. Partial Failures In batch operations, don't let one failure abort everything. Track successes and failures separately. ### 4. Preserve Context Chain exceptions to maintain the full error trail for debugging. ## Quick Start ```python def fetch_page(url: str, page_size: int) -> Page: if not url: raise ValueError("'url' is required") if not 1 <= page_size <= 100: raise ValueError(f"'page_size' must be 1-100, got {page_size}") # Now safe to proceed... ``` ## Fundamental Patterns ### Pattern 1: Early Input Validation Validate all inputs at API boundaries before any processing begins. ```python def process_order( order_id: str, quantity: int, discount_percent: float, ) -> OrderResult: """Process an order with validation.""" # Validate required fields if not order_id: raise ValueError("'order_id' is required") # Validate ranges if quantity <= 0: raise ValueError(f"'quantity' must be positive, got {quantity}")