Path parameters in FastAPI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a path parameter in FastAPI?

A path parameter is a part of the URL path that acts as a variable. It lets you capture values from the URL and use them in your code, like getting an item ID from the URL.

beginner

How do you define a path parameter in a FastAPI route?

You add a variable name inside curly braces in the route path, like /items/{item_id}. Then, you add a function parameter with the same name to receive the value.

intermediate

Can path parameters have types in FastAPI? How?

Yes! You can specify the type of a path parameter by adding a type hint in the function parameter, like item_id: int. FastAPI will convert the value and check the type automatically.

intermediate

What happens if a path parameter value does not match the expected type in FastAPI?

FastAPI returns a 422 error (Unprocessable Entity) because the value cannot be converted to the expected type. This helps catch errors early and keeps your API safe.

beginner

Why are path parameters useful in building APIs?

They let you create dynamic URLs that can handle many different inputs, like fetching different items by ID. This makes your API flexible and easy to use.

How do you declare a path parameter named 'user_id' in FastAPI?

A Using /users/user_id in the route and user_id as a function parameter

B Using /users/{user_id} in the route and user_id as a function parameter

C Using /users/:user_id in the route and user_id as a function parameter

D Using /users?user_id in the route and user_id as a function parameter

Path parameters are declared inside curly braces in the route path, like /users/{user_id}.

What type hint would you use for a numeric path parameter 'item_id'?

A int

B float

C str

D bool

Use int to indicate the parameter should be an integer number.

What response does FastAPI give if a path parameter value cannot be converted to the expected type?

A 422 Unprocessable Entity

B 404 Not Found

C 200 OK

D 500 Internal Server Error

FastAPI returns a 422 error when the path parameter value type is invalid.

Which of these is a valid path parameter in FastAPI?

A /products?product_id

B /products/product_id

C /products/{product_id}

D /products/:product_id

Curly braces {} define path parameters in FastAPI routes.

Why use path parameters instead of query parameters for resource IDs?

A Query parameters are required

B Query parameters are faster

C Path parameters cannot be typed

D Path parameters make URLs cleaner and more RESTful

Path parameters create clean, meaningful URLs that follow REST principles.

Explain how to create a FastAPI route that accepts a path parameter and uses it inside the function.

Think about how the URL and function connect.

Describe what happens when a client sends a wrong type for a path parameter in FastAPI.

Focus on error handling and type safety.