Path parameters in FastAPI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a path parameter named 'item_id' in the route.

FastAPI

from fastapi import FastAPI
app = FastAPI()

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

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

A"{item_id}"

B"item_id"

C"<item_id>"

D"[item_id]"

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes without braces like 'item_id' instead of '{item_id}'.

Using angle brackets or square brackets instead of curly braces.

In FastAPI, path parameters are defined using curly braces in the route path, like '/items/{item_id}'.

2fill in blank

medium

Complete the code to declare the type of the path parameter 'user_id' as string.

FastAPI

from fastapi import FastAPI
app = FastAPI()

@app.get("/users/{user_id}")
async def read_user(user_id: [1]):
    return {"user_id": user_id}

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

Aint

Bfloat

Cstr

Dbool

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'int' when the parameter should be a string.

Omitting the type annotation.

To specify a string path parameter in FastAPI, use 'str' as the type annotation.

3fill in blank

hard

Fix the error in the path parameter declaration to correctly capture 'order_id' as an integer.

FastAPI

from fastapi import FastAPI
app = FastAPI()

@app.get("/orders/[1]")
async def read_order(order_id: int):
    return {"order_id": order_id}

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

A"order_id"

B"[order_id]"

C"<order_id>"

D"{order_id}"

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes without braces around the parameter name.

Using angle or square brackets instead of curly braces.

Path parameters must be enclosed in curly braces in the route path to be recognized by FastAPI.

4fill in blank

hard

Fill both blanks to create a path parameter 'category' of type string and return it in the response.

FastAPI

from fastapi import FastAPI
app = FastAPI()

@app.get("/categories/[1]")
async def read_category(category: [2]):
    return {"category": category}

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

A{category}

Bint

Cstr

Dfloat

Attempts:

3 left

💡 Hint

Common Mistakes

Not using curly braces in the route path.

Using the wrong type annotation like 'int' or 'float'.

The path parameter must be in curly braces in the route, and the type annotation should be 'str' for a string.

5fill in blank

hard

Fill all three blanks to define a path parameter 'product_id' as an integer and return it in a dictionary with key 'product'.

FastAPI

from fastapi import FastAPI
app = FastAPI()

@app.get("/products/[1]")
async def read_product([2]: [3]):
    return {"product": [2]

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

A{product_id}

Bproduct_id

Cint

Dstr

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatch between path parameter name and function parameter name.

Wrong type annotation like 'str' instead of 'int'.

The path parameter must be in curly braces in the route, the function parameter name must match, and the type should be 'int' for an integer.

Practice

1. What is the purpose of path parameters in FastAPI?

easy

A. To send data only in the request body

B. To define static routes without variables

C. To capture values directly from the URL path

D. To handle only query string parameters

Solution

1. Step 1: Understand what path parameters do

   Path parameters allow the API to accept dynamic values from the URL path itself, making routes flexible.

2. Step 2: Compare with other data sources

   Unlike query parameters or request bodies, path parameters are part of the URL path, not optional or in the body.

3. Final Answer:

   To capture values directly from the URL path -> Option C

4. Quick Check:

   Path parameters = URL path values [OK]

Hint: Path parameters are always inside curly braces {} in the URL [OK]

Common Mistakes:

• Confusing path parameters with query parameters
• Thinking path parameters come from request body
• Assuming path parameters are optional by default

2. Which of the following is the correct way to declare a path parameter named item_id in FastAPI?

easy

A. @app.get("/items/:item_id")

B. @app.get("/items/item_id")

C. @app.get("/items/<item_id>")

D. @app.get("/items/{item_id}")

Solution

1. Step 1: Recall FastAPI path parameter syntax

   FastAPI uses curly braces {} to declare path parameters inside route strings.

2. Step 2: Identify the correct syntax

   Only @app.get("/items/{item_id}") uses curly braces correctly: "/items/{item_id}".

3. Final Answer:

   @app.get("/items/{item_id}") -> Option D

4. Quick Check:

   Curly braces {} = path parameters [OK]

Hint: Use curly braces {} around parameter names in route paths [OK]

Common Mistakes:

• Using quotes or angle brackets instead of curly braces
• Forgetting to wrap parameter name in braces
• Using colon syntax like other frameworks

3. Given this FastAPI code snippet, what will be the output when accessing /users/42?

from fastapi import FastAPI
app = FastAPI()

@app.get("/users/{user_id}")
async def read_user(user_id: int):
    return {"user_id": user_id}

medium

A. {"user_id": 42}

B. TypeError because user_id is not a string

C. 404 Not Found error

D. {"user_id": "42"}

Solution

1. Step 1: Understand parameter type conversion

   The path parameter user_id is declared as int, so FastAPI converts the string "42" from the URL to integer 42.

2. Step 2: Check the returned JSON

   The function returns a dictionary with key "user_id" and value 42 as an integer, which FastAPI converts to JSON.

3. Final Answer:

   {"user_id": 42} -> Option A

4. Quick Check:

   Path param type int converts "42" to 42 [OK]

Hint: Check parameter type hints to know output data type [OK]

Common Mistakes:

• Assuming path parameters are always strings
• Expecting a 404 error without reason
• Confusing JSON string with Python dict

4. What is wrong with this FastAPI path parameter code?

from fastapi import FastAPI
app = FastAPI()

@app.get("/products/{product_id}")
async def get_product(product_id):
    return {"product": product_id}

medium

A. Function must be synchronous, not async

B. Missing type annotation for product_id

C. Incorrect route path syntax

D. Return statement must be a string, not dict

Solution

1. Step 1: Check function parameter declaration

   The parameter product_id lacks a type hint, so FastAPI treats it as a string by default but it's best practice to specify type.

2. Step 2: Identify the issue

   While the code runs, missing type annotation can cause unexpected behavior or lack of validation.

3. Final Answer:

   Missing type annotation for product_id -> Option B

4. Quick Check:

   Always add type hints for path parameters [OK]

Hint: Always add type hints to path parameters for validation [OK]

Common Mistakes:

• Ignoring type hints thinking they are optional
• Confusing async with sync function requirements
• Thinking route path syntax is wrong when it is correct

5. You want to create a FastAPI route that accepts two path parameters: category (string) and item_id (integer). Which of the following is the correct way to define this route and function?

hard

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

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

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

D. @app.get("/items/{category}/{item_id}")
def read_item(category: str, item_id: int):
return {"category": category, "item_id": item_id}

Solution

1. Step 1: Match path parameters with function parameters

   The route declares two path parameters in order: category then item_id. The function parameters must match this order and names.

2. Step 2: Check type annotations and async usage

   @app.get("/items/{category}/{item_id}") async def read_item(category: str, item_id: int): return {"category": category, "item_id": item_id} correctly uses type hints (str and int) and async function, which is recommended in FastAPI.

3. Final Answer:

   @app.get("/items/{category}/{item_id}") async def read_item(category: str, item_id: int): return {"category": category, "item_id": item_id} -> Option A

4. Quick Check:

   Order and types must match route parameters [OK]

Hint: Order and names of parameters must match route path [OK]

Common Mistakes:

• Swapping parameter order in function
• Omitting type hints for path parameters
• Using sync function without reason