FastAPI – GET Endpoints and JSON Responses

This document demonstrates how to define multiple GET endpoints in FastAPI, return JSON responses, and use path parameters to retrieve specific data from an in-memory dataset.

Example Application

Create or update main.py with the following content:

from fastapi import FastAPI

app = FastAPI()

users = [
    {"name": "abbas", "age": 20},
    {"name": "mmd", "age": 37},
    {"name": "asghar", "age": 19},
]


@app.get("/")
def root_dir():
    return {"message": "API is working"}


@app.get("/users")
def get_users():
    return users


@app.get("/user/{name_input}")
def get_user_by_name(name_input: str):
    for item in users:
        if item["name"] == name_input:
            return {"information": item}
    return {"message": "User not found"}

Code Overview

Application Initialization

app = FastAPI()

Initializes the FastAPI application instance.

In-Memory Data Store

users = [
    {"name": "abbas", "age": 20},
    {"name": "mmd", "age": 37},
    {"name": "asghar", "age": 19},
]

Simulates a database using a Python list
Each user is represented as a JSON-compatible dictionary
Suitable for development and testing purposes

Defined Endpoints

Root Endpoint

GET /

Response:

{
  "message": "API is working"
}

Used as a health check or readiness probe.

Get All Users

GET /users

Response:

[
  {"name": "abbas", "age": 20},
  {"name": "mmd", "age": 37},
  {"name": "asghar", "age": 19}
]

Returns the full list of users as JSON.

Get User by Name (Path Parameter)

GET /user/{name_input}

Example Request:

GET /user/abbas

Successful Response:

{
  "information": {
    "name": "abbas",
    "age": 20
  }
}

Failure Response:

{
  "message": "User not found"
}

Path Parameters

name_input is a dynamic path parameter
Automatically validated and converted to str by FastAPI
Used to filter data at runtime

Running the Application

Use uvicorn to start the service:

uvicorn main:app --reload

Best Practices

Use structured JSON responses (key: value) instead of tuples
Validate user input when moving beyond in-memory data
Replace in-memory storage with a database for production
Use proper HTTP status codes (404, 200) in real-world APIs
Separate routing, models, and business logic as the project grows

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