Optional query parameters in FastAPI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an optional query parameter with a default value.

FastAPI

from fastapi import FastAPI
from typing import [1]

app = FastAPI()

@app.get("/items/")
async def read_items(q: [1][str] = None):
    return {"q": q}

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

AList

BOptional

CDict

DSet

Attempts:

3 left

💡 Hint

Common Mistakes

Using List or Dict instead of Optional for optional parameters.

Not importing Optional from typing.

The Optional type from typing allows declaring a query parameter that can be None if not provided.

2fill in blank

medium

Complete the code to import the correct function to declare an optional query parameter with a default value.

FastAPI

from fastapi import FastAPI, [1]

app = FastAPI()

@app.get("/users/")
async def get_users(name: str = [1](None)):
    return {"name": name}

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

AQuery

BDepends

CPath

DBody

Attempts:

3 left

💡 Hint

Common Mistakes

Using Depends or Body instead of Query for query parameters.

Not importing Query from fastapi.

The Query function from FastAPI is used to declare and customize query parameters, including setting default values.

3fill in blank

hard

Fix the error in the code by completing the query parameter declaration to make it optional with a default value.

FastAPI

from fastapi import FastAPI, Query

app = FastAPI()

@app.get("/search/")
async def search_items(q: str = [1]):
    return {"q": q}

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

AQuery(default=None)

BQuery()

CQuery(None)

DQuery(default="")

Attempts:

3 left

💡 Hint

Common Mistakes

Using Query() without arguments makes the parameter required.

Using default empty string instead of None.

Using Query(None) declares the query parameter as optional with a default value of None.

4fill in blank

hard

Fill both blanks to declare an optional integer query parameter with a default value of 10.

FastAPI

from fastapi import FastAPI, [1]

app = FastAPI()

@app.get("/numbers/")
async def get_number(limit: int = [1]([2])):
    return {"limit": limit}

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

AQuery

BDepends

C10

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Using Depends instead of Query.

Using None as default instead of 10.

Use Query to declare the query parameter and set its default value to 10.

5fill in blank

hard

Fill all three blanks to declare an optional string query parameter with a default value and a description.

FastAPI

from fastapi import FastAPI, [1]

app = FastAPI()

@app.get("/products/")
async def list_products(q: str = [2]):
    return {"query": q}

# Use Query with default value "book" and description [3]

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

AQuery

BQuery("book", description="Search term")

C"Search term"

DQuery(default="book", description="Search term")

Attempts:

3 left

💡 Hint

Common Mistakes

Putting description as a separate string instead of inside Query.

Not using named arguments for default and description.

Import Query, then use it with default value and description to declare the optional query parameter.

Practice

1. What does it mean when a query parameter in FastAPI is optional?

easy

A. The parameter is required but can be empty

B. The parameter must always be included in the request

C. The user can choose to include it or not in the request

D. The parameter is ignored by FastAPI

Solution

1. Step 1: Understand optional parameters in APIs

   Optional means the user does not have to provide the parameter for the request to work.

2. Step 2: Apply to FastAPI query parameters

   FastAPI allows parameters to be optional by giving them a default value like None.

3. Final Answer:

   The user can choose to include it or not in the request -> Option C

4. Quick Check:

   Optional query parameter = user choice [OK]

Hint: Optional means user may skip it without error [OK]

Common Mistakes:

• Thinking optional means parameter is always required
• Confusing optional with ignored parameters
• Assuming optional means empty string is required

2. Which of the following is the correct way to declare an optional query parameter named q of type str in FastAPI?

easy

A. def read_items(q: Optional[str] = None):

B. def read_items(q: str = None):

C. def read_items(q: str):

D. def read_items(q: Optional[str]):

Solution

1. Step 1: Recall syntax for optional query parameters

   FastAPI uses Optional[type] with a default value None to mark parameters optional.

2. Step 2: Check each option

   def read_items(q: Optional[str] = None): uses Optional[str] and default None, which is correct syntax.

3. Final Answer:

   def read_items(q: Optional[str] = None): -> Option A

4. Quick Check:

   Optional[str] + = None = correct syntax [OK]

Hint: Use Optional[type] with = None for optional params [OK]

Common Mistakes:

• Omitting the default None value
• Using Optional without import
• Setting type to str without Optional

3. Given this FastAPI endpoint code:

from typing import Optional
from fastapi import FastAPI

app = FastAPI()

@app.get("/items/")
async def read_items(q: Optional[str] = None):
    if q:
        return {"query": q}
    return {"query": "No query"}

What will be the JSON response when the client calls /items/ without any query parameters?

medium

A. {"query": null}

B. {"query": "No query"}

C. An error occurs because q is missing

D. {"query": ""}

Solution

1. Step 1: Understand default value of q

   q is Optional[str] with default None, so if missing, q is None.

2. Step 2: Check the if condition

   If q is None (falsey), the function returns {"query": "No query"}.

3. Final Answer:

   {"query": "No query"} -> Option B

4. Quick Check:

   Missing q returns "No query" [OK]

Hint: Missing optional param uses default None [OK]

Common Mistakes:

• Expecting error when param is missing
• Assuming null is returned instead of string
• Confusing empty string with None

4. Identify the error in this FastAPI endpoint code that tries to make q optional:

from fastapi import FastAPI

app = FastAPI()

@app.get("/search/")
def search(q: str = None):
    return {"q": q}

medium

A. q should be typed as Optional[str] when default is None

B. Function must be async to use optional parameters

C. Missing import of Optional from typing

D. Default value None is not allowed for query parameters

Solution

1. Step 1: Check parameter typing and default

   q has type str but default None, which conflicts because None is not str.

2. Step 2: Correct typing for optional parameter

   Use Optional[str] from typing to allow None as a valid default.

3. Final Answer:

   q should be typed as Optional[str] when default is None -> Option A

4. Quick Check:

   Type must match default None with Optional[str] [OK]

Hint: Match type with default None using Optional[type] [OK]

Common Mistakes:

• Not importing Optional but using it
• Making function async unnecessarily
• Using None default without Optional type

5. You want to create a FastAPI endpoint that accepts an optional integer query parameter page with a default of 1, but if the user sends page=0, it should return an error. How would you declare page to achieve this behavior?

hard

A. page: Optional[int] = 1 with extra validation to reject 0

B. page: int without default and require user to send page > 0

C. page: Optional[int] = None and set page = 1 inside function if None

D. page: int = 1 and check inside function if page == 0 to raise error

Solution

1. Step 1: Understand default and validation needs

   Default 1 means page is not optional, but user can omit it to get 1.

2. Step 2: Handle invalid value 0

   Use int with default 1, then inside function check if page == 0 and raise error.

3. Final Answer:

   page: int = 1 and check inside function if page == 0 to raise error -> Option D

4. Quick Check:

   Default + validation inside function = page: int = 1 and check inside function if page == 0 to raise error [OK]

Hint: Use default param + check value inside function [OK]

Common Mistakes:

• Making page Optional[int] = 1 (invalid syntax)
• Not validating 0 value inside function
• Requiring page without default when default needed