Automatic API documentation (Swagger UI) in FastAPI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the FastAPI class needed to create an app.

FastAPI

from fastapi import [1]

app = [1]()

Drag options to blanks, or click blank then click option'

AResponse

BFastAPI

CRequest

DDepends

Attempts:

3 left

💡 Hint

Common Mistakes

Importing Request or Response instead of FastAPI.

Trying to create app without importing FastAPI.

The FastAPI class is imported to create the app instance. This is the main entry point for your API.

2fill in blank

medium

Complete the code to define a GET endpoint that returns a welcome message.

FastAPI

@app.[1]("/")
async def root():
    return {"message": "Welcome to FastAPI!"}

Drag options to blanks, or click blank then click option'

Aget

Bpost

Cput

Ddelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using @app.post or other HTTP methods instead of @app.get.

Missing the decorator entirely.

The @app.get decorator defines a GET HTTP method endpoint. This is used to retrieve data.

3fill in blank

hard

Fix the error in the code to enable automatic API docs with Swagger UI.

FastAPI

from fastapi import FastAPI

app = FastAPI(docs_url=[1])

@app.get("/items/{item_id}")
async def read_item(item_id: int):
    return {"item_id": item_id}

Drag options to blanks, or click blank then click option'

ANone

B"/swagger"

C"/docs"

DFalse

Attempts:

3 left

💡 Hint

Common Mistakes

Setting docs_url to None disables docs.

Using incorrect URL like '/swagger' which is not default.

Setting docs_url to False disables docs.

The default Swagger UI docs URL is '/docs'. Setting docs_url to '/docs' enables the automatic API documentation.

4fill in blank

hard

Fill both blanks to customize the OpenAPI title and version in the FastAPI app.

FastAPI

app = FastAPI(title=[1], version=[2])

Drag options to blanks, or click blank then click option'

A"My API"

B"1.0.0"

C"API Version"

D"v1"

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-string values for title or version.

Confusing title with version strings.

You can customize the API documentation by setting the title and version parameters when creating the FastAPI app.

5fill in blank

hard

Fill all three blanks to add a description, contact email, and license info to the OpenAPI docs.

FastAPI

app = FastAPI(
    description=[1],
    contact=[2],
    license_info=[3]
)

Drag options to blanks, or click blank then click option'

A"This API manages items."

B{"email": "[e-mail]"}

C{"name": "MIT"}

D"API for items management"

Attempts:

3 left

💡 Hint

Common Mistakes

Passing contact or license_info as strings instead of dictionaries.

Omitting required keys in contact or license_info.

FastAPI allows adding extra metadata like description, contact, and license_info to the OpenAPI docs by passing these parameters as strings or dictionaries.

Practice

1. What is the default URL path where FastAPI serves the automatic API documentation using Swagger UI?

easy

A. /docs

B. /swagger

C. /api-docs

D. /documentation

Solution

1. Step 1: Understand FastAPI default docs path

   FastAPI automatically provides Swagger UI documentation at the path '/docs' by default.

2. Step 2: Compare options with default path

   Among the options, only '/docs' matches the default URL for Swagger UI in FastAPI.

3. Final Answer:

   /docs -> Option A

4. Quick Check:

   Default Swagger UI docs path = /docs [OK]

Hint: Remember: FastAPI docs are at /docs by default [OK]

Common Mistakes:

• Confusing /swagger with /docs
• Assuming /api-docs is default
• Thinking documentation is at root /

2. Which of the following code snippets correctly imports and creates a FastAPI app that will have automatic Swagger UI documentation?

easy

A. import fastapi
app = fastapi.App()

B. from fastapi import API
app = API()

C. from fastapi import FastAPI
app = FastAPI()

D. import FastAPI
app = FastAPI()

Solution

1. Step 1: Check correct import and app creation

   The correct import is 'from fastapi import FastAPI' and app is created by calling FastAPI().

2. Step 2: Validate each option

   from fastapi import FastAPI app = FastAPI() matches the correct syntax. Options A, C, and D have wrong imports or class names.

3. Final Answer:

   from fastapi import FastAPI\napp = FastAPI() -> Option C

4. Quick Check:

   Correct import and app creation = from fastapi import FastAPI app = FastAPI() [OK]

Hint: FastAPI app is created by FastAPI() after correct import [OK]

Common Mistakes:

• Using wrong import names like API or App
• Trying to import FastAPI with capital letter as module
• Calling wrong constructor names

3. Given this FastAPI code snippet, what will you see when you open http://localhost:8000/docs in your browser?

from fastapi import FastAPI
app = FastAPI()

@app.get("/hello")
def say_hello():
    return {"message": "Hello, world!"}

medium

A. A 404 Not Found error because /docs is not defined

B. A plain JSON response with {"message": "Hello, world!"}

C. A blank page with no content

D. An interactive Swagger UI showing the /hello GET endpoint with a Try it out button

Solution

1. Step 1: Understand FastAPI automatic docs behavior

   FastAPI automatically generates Swagger UI at /docs showing all defined endpoints.

2. Step 2: Analyze the given code

   The code defines a GET endpoint /hello. The docs page will list this endpoint with interactive testing.

3. Final Answer:

   An interactive Swagger UI showing the /hello GET endpoint with a Try it out button -> Option D

4. Quick Check:

   FastAPI auto docs show endpoints interactively at /docs [OK]

Hint: Open /docs to see interactive API docs with all endpoints [OK]

Common Mistakes:

• Expecting JSON response at /docs instead of UI
• Thinking /docs must be manually coded
• Confusing /docs with endpoint paths

4. You wrote this FastAPI app but when you visit /docs, you get a 404 error. What is the likely cause?

from fastapi import FastAPI
app = FastAPI()

@app.get("/items")
def read_items():
    return [{"item_id": 1}]

# You run the app with: uvicorn main:app --port 8000 --host 0.0.0.0

# But /docs returns 404

medium

A. You are running the app with the wrong module or app name

B. The endpoint /items is missing

C. You need to add extra code to enable /docs

D. You forgot to import FastAPI

Solution

1. Step 1: Check the run command and app reference

   The command 'uvicorn main:app' requires a file named main.py with an app variable.

2. Step 2: Identify mismatch causing 404 on /docs

   If the file or app name is wrong, uvicorn won't serve the correct app, so /docs is missing.

3. Final Answer:

   You are running the app with the wrong module or app name -> Option A

4. Quick Check:

   Run command must match file and app names exactly [OK]

Hint: Match uvicorn run command module:app exactly [OK]

Common Mistakes:

• Assuming /docs needs manual enabling
• Forgetting to import FastAPI (but code shows import)
• Thinking missing endpoint causes /docs 404

5. You want to customize the automatic API docs path from the default /docs to /api-docs. Which FastAPI app creation code achieves this?

hard

A. app = FastAPI(swagger_ui_url="/api-docs")

B. app = FastAPI(docs_url="/api-docs")

C. app = FastAPI(openapi_url="/api-docs")

D. app = FastAPI(docs_path="/api-docs")

Solution

1. Step 1: Identify FastAPI parameter for docs path

   The parameter to change Swagger UI docs path is docs_url.

2. Step 2: Match option with correct parameter

   app = FastAPI(docs_url="/api-docs") uses docs_url="/api-docs", which correctly changes the docs path.

3. Final Answer:

   app = FastAPI(docs_url="/api-docs") -> Option B

4. Quick Check:

   Change docs path with docs_url parameter [OK]

Hint: Use docs_url to set custom docs path [OK]

Common Mistakes:

• Using swagger_ui_url which changes UI assets path
• Changing openapi_url affects JSON schema, not docs UI
• Using docs_path which is not a valid parameter