Boolean query parameters in FastAPI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a boolean query parameter in FastAPI.

FastAPI

from fastapi import FastAPI, Query

app = FastAPI()

@app.get("/items/")
async def read_items(available: bool = Query([1])):
    return {"available": available}

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

ATrue

BNone

C"true"

DFalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using string values like "true" or "false" instead of boolean True or False.

Leaving the default as None which is not a boolean.

The default value for a boolean query parameter should be a boolean type like False. Using False sets the default to false.

2fill in blank

medium

Complete the code to make the boolean query parameter optional with a default of None.

FastAPI

from typing import Optional
from fastapi import FastAPI, Query

app = FastAPI()

@app.get("/items/")
async def read_items(available: Optional[bool] = Query([1])):
    return {"available": available}

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

A"false"

BFalse

CNone

DTrue

Attempts:

3 left

💡 Hint

Common Mistakes

Using a boolean default like True or False when the parameter should be optional.

Using string values instead of None for optional parameters.

To make a boolean query parameter optional, set its default to None and use Optional[bool] as the type.

3fill in blank

hard

Fix the error in the code by completing the boolean query parameter declaration correctly.

FastAPI

from fastapi import FastAPI, Query

app = FastAPI()

@app.get("/items/")
async def read_items(available: bool = [1]):
    return {"available": available}

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

AQuery(True)

BQuery("False")

CQuery("true")

DQuery(None)

Attempts:

3 left

💡 Hint

Common Mistakes

Passing string values like "true" or "False" inside Query for boolean parameters.

Passing None without Optional type hint.

The default value inside Query() for a boolean parameter must be a boolean, like True. Using strings causes errors.

4fill in blank

hard

Fill both blanks to declare an optional boolean query parameter with a default of None and a description.

FastAPI

from typing import Optional
from fastapi import FastAPI, Query

app = FastAPI()

@app.get("/items/")
async def read_items(available: Optional[bool] = Query([1], description=[2])):
    return {"available": available}

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

ANone

B"Is the item available?"

CTrue

D"Optional boolean parameter"

Attempts:

3 left

💡 Hint

Common Mistakes

Using a boolean default instead of None for optional parameters.

Passing non-string values as description.

Use None as the default to make the parameter optional. The description should be a string explaining the parameter.

5fill in blank

hard

Fill all three blanks to declare a boolean query parameter with a default, alias, and description.

FastAPI

from fastapi import FastAPI, Query

app = FastAPI()

@app.get("/items/")
async def read_items(
    available: bool = Query(
        default=[1],
        alias=[2],
        description=[3]
    )
):
    return {"available": available}

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

AFalse

B"is_available"

C"Filter items by availability"

DTrue

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-boolean default values.

Using non-string alias or description.

The default is False. The alias is a string used in the query URL. The description explains the parameter.

Practice

1. What does a Boolean query parameter in FastAPI represent?

easy

A. A true or false flag passed in the URL to control API behavior

B. A number used to count API requests

C. A string that describes the API endpoint

D. A list of items sent in the request body

Solution

1. Step 1: Identify the purpose of Boolean query parameters

   Boolean query parameters are flags that can be true or false, used to control how the API behaves.

2. Step 2: Identify the correct description

   Only "A true or false flag passed in the URL to control API behavior" describes a true/false flag passed via URL query parameters.

3. Final Answer:

   A true or false flag passed in the URL to control API behavior -> Option A

4. Quick Check:

   Boolean query parameter = true/false flag [OK]

Hint: Boolean query parameters are true/false flags in the URL [OK]

Common Mistakes:

• Confusing Boolean parameters with numbers or strings
• Thinking Boolean parameters come from request body
• Assuming Boolean parameters are lists

2. Which of the following is the correct way to declare an optional Boolean query parameter in FastAPI?

easy

A. def read_items(active: bool = Query(None)):

B. def read_items(active: Optional[bool] = Query(None)):

C. def read_items(active: str = Query(None)):

D. def read_items(active: int = Query(None)):

Solution

1. Step 1: Recall FastAPI syntax for optional Boolean query parameters

   Use Optional[bool] with Query(None) to allow the parameter to be true, false, or missing.

2. Step 2: Match the correct function signature

   def read_items(active: Optional[bool] = Query(None)): correctly uses Optional[bool] and Query(None) for an optional Boolean query parameter.

3. Final Answer:

   def read_items(active: Optional[bool] = Query(None)): -> Option B

4. Quick Check:

   Optional[bool] with Query(None) = correct syntax [OK]

Hint: Use Optional[bool] with Query(None) for optional Booleans [OK]

Common Mistakes:

• Using bool without Optional for optional parameters
• Using str or int instead of bool
• Omitting Query import or default value

3. Given this FastAPI endpoint code, what will be the output if the URL is /items?active=true?

from fastapi import FastAPI, Query
from typing import Optional

app = FastAPI()

@app.get('/items')
async def read_items(active: Optional[bool] = Query(None)):
    return {"active": active}

medium

A. Error: invalid query parameter

B. {"active": "true"}

C. {"active": null}

D. {"active": true}

Solution

1. Step 1: Understand FastAPI Boolean query parsing

   FastAPI automatically converts query strings like 'true' to Python boolean True.

2. Step 2: Check the returned dictionary

   The function returns {"active": active}, so with active=true in URL, it returns {"active": true} as JSON.

3. Final Answer:

   {"active": true} -> Option D

4. Quick Check:

   Query 'true' converts to True boolean [OK]

Hint: FastAPI converts 'true' string to True boolean automatically [OK]

Common Mistakes:

• Expecting string 'true' instead of boolean true
• Assuming missing parameter returns false
• Thinking it causes an error

4. Identify the error in this FastAPI endpoint that uses a Boolean query parameter:

from fastapi import FastAPI, Query

app = FastAPI()

@app.get('/items')
async def read_items(active: bool = Query()):
    return {"active": active}

medium

A. The return statement must convert active to string

B. Boolean query parameters cannot be used in FastAPI

C. Query() requires a default value for optional parameters

D. The function must be synchronous, not async

Solution

1. Step 1: Check Query parameter usage

   Query() without a default value means the parameter is required. For optional, a default like None is needed.

2. Step 2: Identify the missing default

   Since active is bool and no default is given, FastAPI expects the query parameter always present, else error.

3. Final Answer:

   Query() requires a default value for optional parameters -> Option C

4. Quick Check:

   Query() needs default for optional params [OK]

Hint: Use Query(None) for optional Boolean parameters [OK]

Common Mistakes:

• Omitting default value for optional query parameters
• Thinking async is not allowed
• Trying to convert Boolean to string manually

5. You want to create a FastAPI endpoint that filters items by an optional Boolean query parameter available. If available is true, return only available items; if false, only unavailable items; if missing, return all items. Which code correctly implements this behavior?

hard

A. from fastapi import FastAPI, Query
from typing import Optional

app = FastAPI()

items = [{"name": "item1", "available": True}, {"name": "item2", "available": False}]

@app.get('/items')
async def read_items(available: Optional[bool] = Query(None)):
if available is None:
return items
return [item for item in items if item["available"] == available]

B. from fastapi import FastAPI

app = FastAPI()

@app.get('/items')
async def read_items(available: bool = False):
return {"available": available}

C. from fastapi import FastAPI, Query

app = FastAPI()

@app.get('/items')
async def read_items(available: bool = Query()):
return {"available": available}

D. from fastapi import FastAPI, Query
from typing import Optional

app = FastAPI()

@app.get('/items')
async def read_items(available: Optional[str] = Query(None)):
return {"available": available}

Solution

1. Step 1: Analyze the required filtering behavior

   If available is None, return all items; else filter by matching available status.

2. Step 2: Check code correctness

   from fastapi import FastAPI, Query from typing import Optional app = FastAPI() items = [{"name": "item1", "available": True}, {"name": "item2", "available": False}] @app.get('/items') async def read_items(available: Optional[bool] = Query(None)): if available is None: return items return [item for item in items if item["available"] == available] uses Optional[bool] with Query(None) and filters items correctly based on available value.

3. Final Answer:

   from fastapi import FastAPI, Query from typing import Optional app = FastAPI() items = [{"name": "item1", "available": True}, {"name": "item2", "available": False}] @app.get('/items') async def read_items(available: Optional[bool] = Query(None)): if available is None: return items return [item for item in items if item["available"] == available] -> Option A

4. Quick Check:

   Optional[bool] with filtering logic = correct [OK]

Hint: Use Optional[bool] and check None to handle missing query param [OK]

Common Mistakes:

• Using bool without Optional for optional parameter
• Not filtering items based on Boolean value
• Using string type instead of Boolean