FastAPI Interview Questions and Answers: Everything You Need to Know

FastAPI is a modern web framework for building APIs with Python 3.7+ based on standard Python type hints. It is known for its high performance and ease of use, making it a popular choice among developers. If you’re preparing for a FastAPI interview, here are some common questions you might encounter along with their answers.

Basics of FastAPI: Features and Framework

1. What is FastAPI?

• FastAPI is a modern web framework for building APIs with Python 3.7+.
• It is based on standard Python type hints, which enables automatic data validation and API documentation generation.
• FastAPI is known for its high performance, thanks to its use of asynchronous programming with Python’s async and await keywords.

2. How does FastAPI compare to other web frameworks like Flask and Django?

• FastAPI is more modern and performs better than Flask and Django due to its use of asynchronous programming and type hints.
• FastAPI provides automatic data validation and API documentation generation, which reduces boilerplate code.

3. What are some key features of FastAPI?

• Automatic validation of request data.
• Automatic generation of interactive API documentation.
• Dependency injection system for organizing code.
• Support for WebSocket APIs.
• High performance due to asynchronous programming.

Uses and Application of FastAPI

1. How do you define a route in FastAPI?

• You can define a route in FastAPI using the @app.get, @app.post, @app.put, @app.delete decorators, followed by the route path.
• For example, @app.get("/items/{item_id}") defines a GET route for retrieving an item with a specific ID.

2. How do you handle request parameters in FastAPI?

• FastAPI automatically handles request parameters using type hints.
• For path parameters, you can define them in the route path, such as {item_id} in /items/{item_id}.
• For query parameters, you can define them as function parameters with default values, such as query_param: int = 0.

3. How do you handle request bodies in FastAPI?

• FastAPI automatically parses request bodies based on the specified data model using Pydantic.
• You can define a data model using Pydantic’s BaseModel class and use it as a function parameter with type hinting.

FastAPI Interview Questions

Introduction to FastAPI

1. What is FastAPI?
   • A) A JavaScript framework
   • B) A web framework for building APIs with Python
   • C) A database management system
   • D) A CSS preprocessor
   Answer: B) A web framework for building APIs with Python
2. Which Python version does FastAPI require?
   • A) Python 2.7
   • B) Python 3.5
   • C) Python 3.7+
   • D) Python 3.9
   Answer: C) Python 3.7+
3. What is a key feature of FastAPI?
   • A) Automatic data validation
   • B) Support for PHP
   • C) Slow performance
   • D) Lack of documentation
   Answer: A) Automatic data validation

Installation and Setup

1. How can you install FastAPI?
   • A) Using npm
   • B) Using pip
   • C) By downloading a zip file
   • D) By cloning a Git repository
   Answer: B) Using pip
2. Which of the following is NOT required for setting up FastAPI?
   • A) Python 3.7+
   • B) Virtual environment
   • C) Flask
   • D) FastAPI package
   Answer: C) Flask
3. What is the purpose of setting up a virtual environment for FastAPI?
   • A) To isolate dependencies
   • B) To make the application run faster
   • C) To avoid using Python 3.7+
   • D) To increase security
   Answer: A) To isolate dependencies

Creating and Running a FastAPI Application

1. How do you create a new FastAPI application?
   • A) By running npm create fastapi-app
   • B) By using a GUI tool
   • C) By running a Python script
   • D) By cloning a Git repository
   Answer: C) By running a Python script
2. How do you run a FastAPI application?
   • A) By double-clicking on the application file
   • B) By using a command-line interface and running uvicorn main:app --reload
   • C) By using a web browser
   • D) By using an IDE
   Answer: B) By using a command-line interface and running uvicorn main:app --reload
3. What is the purpose of the --reload flag when running a FastAPI application?
   • A) To reload the browser automaticallyB) To reload the application automatically when changes are madeC) To reload the server automaticallyD) To reload the virtual environment
   Answer: B) To reload the application automatically when changes are made

Middleware

1. What is middleware in FastAPI?
   • A) A way to define routes
   • B) A way to handle request and response objects
   • C) A way to inject dependencies
   • D) A way to modify requests and responses before they reach the route handler
   Answer: D) A way to modify requests and responses before they reach the route handler
2. How do you define middleware in FastAPI?
   • A) By using the @middleware decorator
   • B) By defining a function that takes request and call_next parameters
   • C) By using the middleware attribute in the application configuration
   • D) By using the add_middleware method
   Answer: B) By defining a function that takes request and call_next parameters
3. What is the purpose of middleware in FastAPI?
   • A) To define routes
   • B) To handle request and response objects
   • C) To inject dependencies
   • D) To perform operations before and after request handlers
   Answer: D) To perform operations before and after request handlers

Authentication and Authorization

1. How do you implement authentication in FastAPI?
   • A) By using the @authenticate decorator
   • B) By using the Auth class
   • C) By using third-party authentication libraries
   • D) By using the @depends decorator
   Answer: C) By using third-party authentication libraries
2. What is the purpose of authentication in FastAPI?
   • A) To define routes
   • B) To handle request and response objects
   • C) To verify the identity of the user
   • D) To inject dependencies
   Answer: C) To verify the identity of the user
3. How do you implement authorization in FastAPI?
   • A) By using the @authorize decorator
   • B) By using the Authorization class
   • C) By using third-party authorization libraries
   • D) By using the @depends decorator
   Answer: C) By using third-party authorization libraries

Error Handling

1. How do you handle errors in FastAPI?
   • A) By using try-except blocks
   • B) By defining error handlers using the @app.exception_handler decorator
   • C) By using the raise statement
   • D) By using the @error_handler decorator
   Answer: B) By defining error handlers using the @app.exception_handler decorator
2. What is the purpose of error handling in FastAPI?
   • A) To define routes
   • B) To handle request and response objects
   • C) To handle errors and exceptions that occur during request processing
   • D) To inject dependencies
   Answer: C) To handle errors and exceptions that occur during request processing
3. How do you return custom error responses in FastAPI?
   • A) By raising an exception with a custom messageB) By using the HTTPException classC) By using the @error_response decoratorD) By modifying the response object directly
   Answer: B) By using the HTTPException class