Error Basics

Learn essential concepts of error basics in FastAPI.

What You'll Learn

This section covers error handling, including:

• HTTPException for API errors

• Custom exception classes

• Exception handlers for centralized error processing

• Validation error responses

• Error logging and monitoring

• Best practices for error design

Core Concepts

Proper error handling:

• Returns appropriate HTTP status codes

• Provides clear, actionable error messages

• Logs errors for debugging

• Never exposes sensitive details

• Handles edge cases gracefully

Basic HTTPException Example

from fastapi import FastAPI, HTTPException
from fastapi import status

app = FastAPI()

@app.get("/items/{item_id}")
async def get_item(item_id: int):
    if item_id < 1:
        raise HTTPException(
            status_code=status.HTTP_400_BAD_REQUEST,
            detail="Item ID must be positive"
        )
    if item_id > 1000:
        raise HTTPException(
            status_code=status.HTTP_404_NOT_FOUND,
            detail="Item not found"
        )
    return {"item_id": item_id}

Exception Handler Example

from fastapi.responses import JSONResponse

@app.exception_handler(ValueError)
async def value_error_handler(request, exc):
    return JSONResponse(
        status_code=400,
        content={"error": "Invalid value", "detail": str(exc)}
    )

Real-World Usage

Error handling is critical for:

• **API reliability**: Gracefully handle failures

• **Client feedback**: Clear messages for debugging

• **Monitoring**: Track error patterns

• **Security**: Don't expose internal details

• **Compliance**: Meet error logging requirements

🔑 Key Takeaways

• ✅ Understand the purpose of error basics

• ✅ Know when to apply this pattern

• ✅ Follow best practices consistently

• ✅ Test thoroughly in production scenarios

Next step: Explore the advanced section for production patterns and optimization techniques.