Environment variable management in FastAPI - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

How does FastAPI load environment variables with Pydantic BaseSettings?

Given this FastAPI settings class using Pydantic's BaseSettings, what will be the value of settings.api_key if the environment variable API_KEY is set to secret123?

FastAPI

from pydantic import BaseSettings

class Settings(BaseSettings):
    api_key: str

settings = Settings()

A "api_key"

B "secret123"

C Raises a ValidationError because no default is set

D "" (empty string)

💡 Hint

Pydantic BaseSettings automatically reads environment variables matching attribute names in uppercase.

The Settings class inherits from BaseSettings, which reads environment variables matching the attribute names in uppercase. Since API_KEY is set in the environment, settings.api_key will have the value "secret123".

📝 Syntax

intermediate

Identify the syntax error in this FastAPI environment variable loading code

Which option contains the correct way to define a Pydantic BaseSettings class to load an environment variable DATABASE_URL?

FastAPI

from pydantic import BaseSettings

class Settings(BaseSettings):
    database_url: str

settings = Settings()

A

class Settings(BaseSettings):
    database_url: str

settings = Settings()

B

class Settings(BaseSettings):
    database_url = str

settings = Settings()

C

class Settings(BaseSettings):
    database_url: str = None

settings = Settings()

D

class Settings(BaseSettings):
    database_url: str

settings = Settings

💡 Hint

Check how type annotations and instantiation are done.

Option A correctly uses a type annotation database_url: str and creates an instance with Settings(). Option A assigns the type to the variable, which is incorrect. Option A sets a default None which is invalid for a required str without Optional. Option A misses parentheses when instantiating.

❓ state_output

advanced

What is the output when environment variable is missing and no default is set?

Consider this FastAPI settings class. What happens when you run settings = Settings() but the environment variable SECRET_KEY is not set?

FastAPI

from pydantic import BaseSettings

class Settings(BaseSettings):
    secret_key: str

settings = Settings()

A settings.secret_key is set to 'secret_key'

B settings.secret_key is set to an empty string

C settings.secret_key is set to None

D Raises pydantic.ValidationError because secret_key is required but missing

💡 Hint

Required fields without defaults must be provided by environment or raise error.

Since secret_key is required and no default is provided, and the environment variable SECRET_KEY is missing, Pydantic raises a ValidationError when creating the Settings instance.

🔧 Debug

advanced

Why does this FastAPI app fail to read environment variables correctly?

This FastAPI app uses Pydantic BaseSettings but always returns default values instead of environment variables. What is the likely cause?

FastAPI

from fastapi import FastAPI
from pydantic import BaseSettings

class Settings(BaseSettings):
    app_name: str = "MyApp"

settings = Settings()

app = FastAPI()

@app.get("/")
def read_root():
    return {"app_name": settings.app_name}

A The app_name field must be Optional[str] to read environment variables

B BaseSettings does not support environment variables by default

C Environment variables are not loaded because the .env file is missing or not in the working directory

D FastAPI requires special middleware to read environment variables

💡 Hint

Check if environment variables are actually available to the app process.

BaseSettings reads environment variables from the OS environment or a .env file in the working directory. If the .env file is missing or environment variables are not set, default values are used. The likely cause is missing environment variables or .env file.

🧠 Conceptual

expert

How does Pydantic BaseSettings prioritize environment variables and defaults?

Given a Pydantic BaseSettings class with a field timeout: int = 30, and an environment variable TIMEOUT=60 set, what will be the value of settings.timeout after instantiation?

FastAPI

from pydantic import BaseSettings

class Settings(BaseSettings):
    timeout: int = 30

settings = Settings()

A 60, because environment variables override default values

B 30, because default values always take precedence over environment variables

C None, because the environment variable is ignored

D Raises ValidationError because environment variables cannot override defaults

💡 Hint

Think about how BaseSettings merges environment variables with defaults.

Pydantic BaseSettings uses environment variables to override default values. Since TIMEOUT=60 is set in the environment, settings.timeout will be 60, not the default 30.