Dependencies with parameters in FastAPI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a dependency with parameters in FastAPI?

A dependency with parameters is a function that accepts arguments and returns a value to be injected into path operations or other dependencies. It allows customizing behavior based on input values.

intermediate

How do you declare a dependency with parameters in FastAPI?

You create a function that takes parameters and returns a callable dependency function. Then you use Depends with a lambda or functools.partial to pass parameters when injecting.

beginner

Why use dependencies with parameters instead of global dependencies?

Dependencies with parameters let you customize the dependency's behavior per request or route, making your code more flexible and reusable.

intermediate

Example: How to pass a parameter to a dependency in FastAPI?

Define a function that returns another function using the parameter. Use Depends with a lambda: e.g., Depends(lambda: get_db(session_id=123)).

beginner

What happens if you forget to pass parameters to a dependency that requires them?

FastAPI will raise an error because it cannot resolve the dependency properly. Parameters must be provided explicitly or via another dependency.

How do you inject a dependency with a parameter in FastAPI?

A Use Depends with a lambda or partial function to pass parameters

B Declare parameters directly in the path operation function

C Use global variables inside the dependency function

D FastAPI does not support dependencies with parameters

You pass parameters by wrapping the dependency call in a lambda or partial function inside Depends.

What is the purpose of dependencies with parameters?

A To define global constants

B To make dependencies run faster

C To avoid using Depends in FastAPI

D To customize dependency behavior per request or route

Dependencies with parameters allow you to change how the dependency works depending on input values.

Which of these is a correct way to define a dependency with parameters?

A def get_user(user_id: int): return user_id

B def get_user(user_id: int): def dependency(): return user_id; return dependency

C def get_user(): return user_id

D def get_user(): pass

You define a function that returns another function capturing the parameter.

What happens if a dependency with parameters is used without passing required parameters?

A FastAPI raises an error at runtime

B The dependency uses default parameters automatically

C The dependency is ignored

D The server crashes immediately

FastAPI cannot resolve the dependency and raises an error if parameters are missing.

Which FastAPI feature helps pass parameters to dependencies?

A Middleware

B Path parameters only

C Depends with lambda or functools.partial

D Background tasks

Depends combined with lambda or partial lets you pass parameters to dependencies.

Explain how to create and use a dependency with parameters in FastAPI.

Think about wrapping the dependency function to capture parameters.

Why are dependencies with parameters useful in FastAPI applications?

Consider how parameters help change dependency output.