FastAPI installation and setup - Practice Problems & Coding Challenges

Challenge - 5 Problems

📝 Syntax

intermediate

Correct command to install FastAPI with Uvicorn

Which command correctly installs FastAPI along with Uvicorn for running the server?

A pip install fastapi; uvicorn install

B pip install fastapi-uvicorn

C pip install fastapi --with uvicorn

D pip install fastapi uvicorn

💡 Hint

Think about how Python packages are installed together using pip.

The correct way to install FastAPI and Uvicorn together is by listing both packages separated by a space in one pip install command.

❓ component_behavior

intermediate

Behavior of a minimal FastAPI app

What will be the output when you visit http://localhost:8000/ after running this FastAPI app code?

FastAPI

from fastapi import FastAPI
app = FastAPI()

@app.get('/')
async def read_root():
    return {"message": "Hello, FastAPI!"}

A {"message": "Hello, FastAPI!"}

B Hello, FastAPI!

C 404 Not Found error

D 500 Internal Server Error

💡 Hint

FastAPI returns JSON responses by default from dictionary returns.

The function returns a dictionary, so FastAPI converts it to JSON automatically. The browser will show the JSON string.

🔧 Debug

advanced

Identify the error when running FastAPI app

What error will occur if you run this code and try to start the server with uvicorn main:app --reload?

FastAPI

from fastapi import FastAPI
app = FastAPI()

@app.get('/')
def read_root():
    return "Hello"

A TypeError: FastAPI endpoint must return dict or Response, not str

B No error, server runs and returns plain text 'Hello'

C SyntaxError: missing async keyword

D RuntimeError: Uvicorn not installed

💡 Hint

FastAPI can return strings directly as plain text responses.

FastAPI allows returning strings directly, which it sends as plain text. No error occurs.

🧠 Conceptual

advanced

Purpose of Uvicorn in FastAPI setup

What is the main role of Uvicorn when used with FastAPI?

A It is a database driver required for FastAPI to connect to databases

B It is a frontend framework to build user interfaces for FastAPI apps

C It is an ASGI server that runs the FastAPI app and handles requests asynchronously

D It is a testing tool to check FastAPI app performance

💡 Hint

Think about what runs your app and listens for web requests.

Uvicorn is a lightweight ASGI server that runs FastAPI apps and handles asynchronous web requests.

❓ state_output

expert

Output after modifying FastAPI app with startup event

Given this FastAPI app code, what will be printed to the console when the server starts?

FastAPI

from fastapi import FastAPI
app = FastAPI()

@app.on_event("startup")
async def startup_event():
    print("Server is starting...")

@app.get('/')
async def read_root():
    return {"status": "running"}

A Server is starting...

B No output printed on startup

C Error: on_event decorator not found

D Server is starting...\nGET / 200 OK

💡 Hint

The startup event runs once when the server launches.

The @app.on_event("startup") decorator runs the function when the server starts, printing the message once.

Practice

1. What is the main command to install FastAPI with all optional dependencies for full functionality?

easy

A. pip install fastapi[all]

B. pip install fastapi-core

C. pip install fastapi-full

D. pip install fastapi-basic

Solution

1. Step 1: Understand FastAPI installation options

   FastAPI can be installed with or without optional dependencies. The command with [all] installs everything needed for full features.

2. Step 2: Identify the correct pip command

   The correct command to install FastAPI with all optional dependencies is pip install fastapi[all].

3. Final Answer:

   pip install fastapi[all] -> Option A

4. Quick Check:

   Full install command = pip install fastapi[all] [OK]

Hint: Remember: [all] installs everything FastAPI needs [OK]

Common Mistakes:

• Using pip install fastapi without [all] misses optional tools
• Trying pip install fastapi-core which doesn't exist
• Confusing with pip install fastapi-full or fastapi-basic

2. Which command correctly runs a FastAPI app locally using Uvicorn?

easy

A. uvicorn app:app --reload

B. fastapi run app.py

C. python app.py

D. uvicorn run app.py

Solution

1. Step 1: Identify the tool to run FastAPI apps

   Uvicorn is the ASGI server used to run FastAPI apps locally for testing.

2. Step 2: Use the correct command syntax

   The correct command is uvicorn app:app --reload, where the first 'app' is the Python file name (without .py) and the second 'app' is the FastAPI instance.

3. Final Answer:

   uvicorn app:app --reload -> Option A

4. Quick Check:

   Run FastAPI with uvicorn app:app --reload [OK]

Hint: Use uvicorn with file:instance and --reload for dev [OK]

Common Mistakes:

• Trying to run FastAPI with python app.py directly
• Using wrong uvicorn syntax like 'uvicorn run app.py'
• Confusing fastapi run command which does not exist

3. Given this command run in terminal: uvicorn main:app --reload, what does the --reload flag do?

medium

A. Disables debugging features

B. Automatically restarts the server on code changes

C. Runs the server in production mode

D. Compiles the app to bytecode

Solution

1. Step 1: Understand the purpose of --reload flag

   The --reload flag tells Uvicorn to watch for code changes and restart the server automatically.

2. Step 2: Identify what happens without --reload

   Without --reload, the server runs but does not restart on code edits, making development slower.

3. Final Answer:

   Automatically restarts the server on code changes -> Option B

4. Quick Check:

   --reload means auto restart on code change [OK]

Hint: Reload flag = auto restart server on code edits [OK]

Common Mistakes:

• Thinking --reload enables production mode
• Assuming it disables debugging
• Believing it compiles code instead of reloading

4. You run uvicorn app:app --reload but get an error: ModuleNotFoundError: No module named 'app'. What is the likely cause?

medium

A. Uvicorn is not installed

B. The FastAPI instance is not named 'app' inside the file

C. The Python file named app.py does not exist in the current directory

D. The --reload flag is incompatible with your Python version

Solution

1. Step 1: Understand the error meaning

   The error means Python cannot find a module named 'app', which should be the filename without .py.

2. Step 2: Check the file existence

   If the file app.py is missing or you are in the wrong directory, this error occurs.

3. Final Answer:

   The Python file named app.py does not exist in the current directory -> Option C

4. Quick Check:

   ModuleNotFoundError means missing file/module [OK]

Hint: Check your file name and directory for the module [OK]

Common Mistakes:

• Assuming Uvicorn is not installed causes this error
• Thinking the FastAPI instance name causes ModuleNotFoundError
• Blaming --reload flag for import errors

5. You want to start a new FastAPI project. Which sequence correctly sets up and runs your app locally?

hard

A. pip install fastapi[all] -> create app.py -> uvicorn run app.py

B. pip install uvicorn -> create app.py -> python app.py

C. pip install fastapi -> create app.py -> fastapi run app.py

D. pip install fastapi[all] -> create app.py with FastAPI instance -> uvicorn app:app --reload

Solution

1. Step 1: Install FastAPI with all dependencies

   Use pip install fastapi[all] to get FastAPI and recommended tools like Uvicorn.

2. Step 2: Create your app.py file with a FastAPI instance named 'app'

   This file contains your API code and the FastAPI() instance.

3. Step 3: Run the app locally with Uvicorn and reload

   Use uvicorn app:app --reload to start the server with auto-reload for development.

4. Final Answer:

   pip install fastapi[all] -> create app.py with FastAPI instance -> uvicorn app:app --reload -> Option D

5. Quick Check:

   Install, create app, run with uvicorn --reload [OK]

Hint: Install FastAPI[all], create app.py, run uvicorn app:app --reload [OK]

Common Mistakes:

• Installing only uvicorn without FastAPI
• Trying to run app.py directly with python
• Using wrong uvicorn command syntax