[Solved] This middleware code causes an error:class ErrorMiddleware(BaseHTTPMiddleware): def dispatch(self, request, call_next):... | FastAPI

FastAPI - Middleware and Hooks

This middleware code causes an error:

class ErrorMiddleware(BaseHTTPMiddleware):
    def dispatch(self, request, call_next):
        print("Start")
        response = await call_next(request)
        print("End")
        return response

app.add_middleware(ErrorMiddleware)

What is the error?

Aprint statements are not allowed in middleware.

Bdispatch method must be async to use await inside.

CMiddleware must be added before route definitions.

Ddispatch method should not have parameters.

Step-by-Step Solution

Solution:

Step 1: Check method signature for async usage
dispatch uses await, so it must be declared async.
Step 2: Identify missing async keyword
dispatch is missing async, causing syntax error on await.
Final Answer:
dispatch method must be async to use await inside. -> Option B
Quick Check:
await requires async function [OK]

Quick Trick: Use async def for dispatch when awaiting call_next [OK]

Common Mistakes:

MISTAKES

Forgetting async keyword on dispatch
Misunderstanding middleware method parameters
Thinking print causes errors

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This middleware code causes an error:

Step 1: Check method signature for async usage

Step 2: Identify missing async keyword

Final Answer:

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