[Solved] Analyze this FastAPI dependency code:from fastapi import Depends def get_resource(): resource = open_resource() return resource def fetch_data(res = get_resource()): return res.... | FastAPI

FastAPI - Dependency Injection

Analyze this FastAPI dependency code:

from fastapi import Depends

def get_resource():
    resource = open_resource()
    return resource

def fetch_data(res = get_resource()):
    return res.read()

What is the main issue with this code?

ADependency is called at function definition, not injected per request

BMissing import for Depends

CFunction get_resource does not return anything

Dfetch_data should be async to use dependencies

Step-by-Step Solution

Solution:

Step 1: Identify dependency usage
The function fetch_data uses res = get_resource() as a default parameter, which calls get_resource immediately at definition time.
Step 2: Understand dependency injection
FastAPI expects dependencies to be declared with Depends() so they are called per request, not once at startup.
Step 3: Problem
Calling get_resource() directly means the resource is opened once globally, not per request, breaking dependency injection principles.
Final Answer:
Dependency is called at function definition, not injected per request -> Option A
Quick Check:
Dependency must be wrapped in Depends() [OK]

Quick Trick: Use Depends() to defer dependency calls per request [OK]

Common Mistakes:

MISTAKES

Calling dependency functions directly instead of using Depends
Assuming default parameters are evaluated per request
Ignoring the need for per-request resource management

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Analyze this FastAPI dependency code:

Step 1: Identify dependency usage

Step 2: Understand dependency injection

Step 3: Problem

Final Answer:

Quick Check:

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