Response model exclude and include in FastAPI - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output when using response_model_exclude in FastAPI?

Consider this FastAPI endpoint using a Pydantic model with response_model_exclude to hide some fields. What will the JSON response include?

FastAPI

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class User(BaseModel):
    id: int
    username: str
    email: str

@app.get("/user", response_model=User, response_model_exclude={"email"})
def get_user():
    return User(id=1, username="alice", email="[e-mail]")

A {"id": 1, "username": "alice"}

B {"id": 1, "username": "alice", "email": "[e-mail]"}

C {"username": "alice", "email": "[e-mail]"}

D {"id": 1, "email": "[e-mail]"}

💡 Hint

Think about which fields are excluded from the response model.

The response_model_exclude option tells FastAPI to remove specified fields from the response. Here, email is excluded, so it won't appear in the JSON output.

❓ component_behavior

intermediate

How does response_model_include affect the FastAPI response?

Given this FastAPI endpoint, what fields will appear in the JSON response when using response_model_include?

FastAPI

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class Product(BaseModel):
    id: int
    name: str
    price: float
    description: str

@app.get("/product", response_model=Product, response_model_include={"id", "name"})
def get_product():
    return Product(id=10, name="Book", price=12.99, description="A nice book")

A {"id": 10, "price": 12.99, "description": "A nice book"}

B {"id": 10, "name": "Book"}

C {"id": 10, "name": "Book", "price": 12.99}

D {"name": "Book", "price": 12.99, "description": "A nice book"}

💡 Hint

Only the fields listed in response_model_include will be shown.

The response_model_include option limits the response to only the specified fields. Here, only id and name are included.

📝 Syntax

advanced

What error occurs with incorrect response_model_exclude syntax?

Which option shows the error raised by this FastAPI endpoint with wrong response_model_exclude syntax?

FastAPI

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class Item(BaseModel):
    id: int
    name: str
    price: float

@app.get("/item", response_model=Item, response_model_exclude=["price"])
def get_item():
    return Item(id=5, name="Pen", price=1.5)

A No error, runs correctly

B SyntaxError: invalid syntax

C TypeError: unhashable type: 'list'

D ValueError: field 'price' not found

💡 Hint

Check the type expected for response_model_exclude.

The response_model_exclude parameter expects a set or dict, not a list. Passing a list causes a TypeError because lists are unhashable.

❓ state_output

advanced

What is the output when combining response_model_include and response_model_exclude?

Given this FastAPI endpoint, what fields will appear in the JSON response?

FastAPI

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class Profile(BaseModel):
    id: int
    username: str
    email: str
    bio: str

@app.get(
    "/profile",
    response_model=Profile,
    response_model_include={"id", "username", "email"},
    response_model_exclude={"email"}
)
def get_profile():
    return Profile(id=2, username="bob", email="[e-mail]", bio="Hello!")

A {"id": 2, "username": "bob", "email": "[e-mail]"}

B {"id": 2, "username": "bob", "bio": "Hello!"}

C {"username": "bob", "email": "[e-mail]", "bio": "Hello!"}

D {"id": 2, "username": "bob"}

💡 Hint

Remember that response_model_exclude removes fields even if included.

When both response_model_include and response_model_exclude are used, FastAPI first includes only the specified fields, then excludes the ones listed. Here, email is included but then excluded, so it is removed.

🔧 Debug

expert

Why does this FastAPI endpoint return all fields despite response_model_exclude?

Analyze this code. Why does the response include all fields even though response_model_exclude is set?

FastAPI

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class Data(BaseModel):
    a: int
    b: int
    c: int

@app.get("/data", response_model=Data, response_model_exclude={"b"})
def get_data():
    return {"a": 1, "b": 2, "c": 3}

A The response includes all fields because the returned value is a dict, not a Pydantic model instance.

B The response includes all fields because <code>response_model_exclude</code> only works with lists, not sets.

C The response includes all fields because <code>response_model_exclude</code> is ignored when returning dicts.

D The response includes all fields because the endpoint is missing a <code>return</code> statement.

💡 Hint

Think about how FastAPI processes the returned data with response models.

FastAPI applies response_model_exclude only when the returned value is an instance of the response model class. Returning a plain dict bypasses this filtering.