Environment variable management in FastAPI

Introduction

Environment variables help keep sensitive data like passwords safe and let you change settings without changing code.

You want to keep API keys secret and not write them in your code.

You need to change database settings when moving from your computer to a server.

You want to set different options for development and production without changing code.

You want to avoid hardcoding passwords or tokens in your FastAPI app.

You want to easily update configuration without redeploying your app.

Syntax

FastAPI

import os

value = os.getenv('VARIABLE_NAME', 'default_value')

Use os.getenv to read environment variables safely.

Provide a default value to avoid errors if the variable is missing.

Examples

Reads the API_KEY environment variable. Returns None if not set.

FastAPI

import os

api_key = os.getenv('API_KEY')

Reads PORT and converts it to an integer. Uses 8000 if PORT is not set.

FastAPI

import os

port = int(os.getenv('PORT', '8000'))

Uses Pydantic's BaseSettings to automatically load environment variables into a settings object.

FastAPI

from pydantic import BaseSettings

class Settings(BaseSettings):
    database_url: str
    secret_key: str

settings = Settings()

Sample Program

This FastAPI app reads the API_KEY environment variable when it starts. If not set, it uses 'no-key-found'. The root URL shows the API key value.

FastAPI

import os
from fastapi import FastAPI

app = FastAPI()

API_KEY = os.getenv('API_KEY', 'no-key-found')

@app.get('/')
async def read_root():
    return {"message": f"Your API key is: {API_KEY}"}

Important Notes

Set environment variables before running your FastAPI app, for example: export API_KEY='mysecret' on Linux/macOS or set API_KEY=mysecret on Windows.

Use python-dotenv package to load variables from a .env file during development.

Never commit secrets like API keys or passwords to your code repository.

Summary

Environment variables keep sensitive info safe and separate from code.

Use os.getenv or Pydantic BaseSettings to access them in FastAPI.

Always provide defaults or handle missing variables to avoid crashes.

Practice

1. What is the main reason to use environment variables in a FastAPI project?

easy

A. To keep sensitive information like API keys out of the code

B. To make the code run faster

C. To store user data permanently

D. To create new API endpoints automatically

Solution

1. Step 1: Understand environment variables purpose

   Environment variables are used to keep sensitive data like passwords or API keys separate from the code to improve security.

2. Step 2: Identify the correct reason in FastAPI context

   FastAPI uses environment variables to avoid hardcoding secrets, which helps keep them safe and flexible.

3. Final Answer:

   To keep sensitive information like API keys out of the code -> Option A

4. Quick Check:

   Environment variables = keep secrets safe [OK]

Hint: Environment variables store secrets, not speed or data [OK]

Common Mistakes:

• Thinking environment variables speed up code
• Confusing environment variables with database storage
• Assuming environment variables create API routes

2. Which of the following is the correct way to get an environment variable named API_KEY using Python's os module in FastAPI?

easy

A. api_key = os.get('API_KEY')

B. api_key = os.getenv('API_KEY')

C. api_key = os.environ.get('API_KEY')()

D. api_key = os.getenv(API_KEY)

Solution

1. Step 1: Recall correct os module function

   The correct function to get environment variables is os.getenv('VAR_NAME').

2. Step 2: Check syntax correctness

   api_key = os.getenv('API_KEY') uses os.getenv('API_KEY') correctly with quotes around the variable name and no extra parentheses.

3. Final Answer:

   api_key = os.getenv('API_KEY') -> Option B

4. Quick Check:

   Use os.getenv('VAR') to get environment variables [OK]

Hint: Use os.getenv('VAR_NAME') with quotes [OK]

Common Mistakes:

• Using os.get instead of os.getenv
• Calling os.environ.get with extra parentheses
• Not quoting the environment variable name

3. Given this FastAPI code snippet using Pydantic's BaseSettings:

from pydantic import BaseSettings

class Settings(BaseSettings):
    app_name: str
    debug_mode: bool = False

settings = Settings()

If the environment variable APP_NAME is set to "MyApp" and DEBUG_MODE is not set, what will settings.app_name and settings.debug_mode be?

medium

A. None and None

B. "MyApp" and True

C. None and False

D. "MyApp" and False

Solution

1. Step 1: Understand BaseSettings behavior

   Pydantic BaseSettings reads environment variables matching attribute names in uppercase by default.

2. Step 2: Check provided environment variables and defaults

   APP_NAME is set to "MyApp", so settings.app_name is "MyApp". DEBUG_MODE is not set, so it uses the default False.

3. Final Answer:

   "MyApp" and False -> Option D

4. Quick Check:

   Env var set = value, missing uses default [OK]

Hint: Unset vars use default values in BaseSettings [OK]

Common Mistakes:

• Assuming missing env vars become True
• Thinking unset vars become None instead of default
• Confusing attribute names with env var names

4. What is wrong with this FastAPI environment variable usage code?

import os

API_KEY = os.getenv('API_KEY')
print(f"API key is {API_KEY.upper()}")

Assuming API_KEY is not set in the environment.

medium

A. It will raise an AttributeError because API_KEY is None

B. It will print 'API key is ' with empty string

C. It will raise a SyntaxError

D. It will print the string 'None'

Solution

1. Step 1: Check os.getenv behavior when var missing

   os.getenv returns None if the environment variable is not set and no default is given.

2. Step 2: Understand what happens calling upper() on None

   Calling None.upper() raises an AttributeError because NoneType has no method upper().

3. Final Answer:

   It will raise an AttributeError because API_KEY is None -> Option A

4. Quick Check:

   None.upper() causes AttributeError [OK]

Hint: Check for None before calling string methods [OK]

Common Mistakes:

• Assuming os.getenv returns empty string if missing
• Expecting no error when calling upper() on None
• Confusing AttributeError with SyntaxError

5. You want to manage environment variables in FastAPI using Pydantic's BaseSettings and ensure a default port of 8000 if PORT is not set. Which code snippet correctly achieves this?

hard

A. class Settings(BaseSettings):
port: int

settings = Settings(port=8000)

B. class Settings(BaseSettings):
port: int

settings = Settings() # default 8000 if missing

C. class Settings(BaseSettings):
port: int = 8000

settings = Settings()

D. class Settings(BaseSettings):
port: str = '8000'

settings = Settings()

Solution

1. Step 1: Define default value in BaseSettings attribute

   Setting port: int = 8000 provides a default if the environment variable PORT is missing.

2. Step 2: Instantiate Settings without arguments

   Calling Settings() reads environment variables or uses defaults if missing, so port will be 8000 if PORT is unset.

3. Final Answer:

   class Settings(BaseSettings): port: int = 8000 settings = Settings() -> Option C

4. Quick Check:

   Default values in BaseSettings = default used if env var missing [OK]

Hint: Set default in class attribute for fallback [OK]

Common Mistakes:

• Not providing default and expecting fallback
• Passing default in constructor instead of attribute
• Using string type for port instead of int