How can I access environment variables in Python?

Accessing Environment Variables in Python

Learn how to effectively read, set, and manage environment variables in Python for flexible and secure application configuration.

Environment variables are a fundamental mechanism for configuring applications, especially in different deployment environments (development, testing, production). They allow you to store sensitive information like API keys, database credentials, or configuration settings outside your codebase, preventing them from being hardcoded. Python provides straightforward ways to interact with these variables. This article will guide you through accessing, setting, and understanding the best practices for using environment variables in your Python projects.

Reading Environment Variables with os.environ

The primary way to interact with environment variables in Python is through the built-in os module, specifically the os.environ dictionary-like object. This object provides access to all environment variables available to the current process.

import os

# Accessing an environment variable
api_key = os.environ.get('MY_API_KEY')

if api_key:
    print(f"API Key found: {api_key}")
else:
    print("MY_API_KEY not set.")

# Accessing all environment variables (for inspection)
# for key, value in os.environ.items():
#     print(f"{key}={value}")

# Accessing a variable that might not exist (with default value)
debug_mode = os.environ.get('DEBUG_MODE', 'False').lower() == 'true'
print(f"Debug Mode: {debug_mode}")

Basic usage of os.environ.get() to read environment variables.

Setting Environment Variables

While it's generally recommended to set environment variables outside your Python script (e.g., in your shell, deployment configuration, or .env files), you can also set them programmatically within your Python code. This can be useful for testing or for child processes.

import os

# Setting a new environment variable
os.environ['NEW_VARIABLE'] = 'Hello World'
print(f"NEW_VARIABLE: {os.environ.get('NEW_VARIABLE')}")

# Modifying an existing environment variable
os.environ['PATH'] = os.environ.get('PATH', '') + os.pathsep + '/usr/local/custom_bin'
print(f"Updated PATH: {os.environ['PATH']}")

# Deleting an environment variable
if 'NEW_VARIABLE' in os.environ:
    del os.environ['NEW_VARIABLE']
    print("NEW_VARIABLE deleted.")
else:
    print("NEW_VARIABLE was not set.")

Setting and deleting environment variables programmatically.

Managing Environment Variables with .env Files

For local development, managing numerous environment variables directly in your shell can become cumbersome. The python-dotenv library provides a convenient way to load variables from a .env file into os.environ.

First, install the library:

pip install python-dotenv

Installing the python-dotenv library.

Next, create a .env file in your project's root directory:

# .env file
DATABASE_URL="postgresql://user:password@host:port/dbname"
SECRET_KEY="supersecretkey123"
DEBUG=True

Example .env file content.

Then, load these variables in your Python script:

import os
from dotenv import load_dotenv

# Load environment variables from .env file
load_dotenv()

# Access variables as usual
db_url = os.environ.get('DATABASE_URL')
secret_key = os.environ.get('SECRET_KEY')
debug_mode = os.environ.get('DEBUG', 'False').lower() == 'true'

print(f"Database URL: {db_url}")
print(f"Secret Key: {secret_key}")
print(f"Debug Mode: {debug_mode}")

Loading environment variables from a .env file using python-dotenv.

Environment Variable Access Flow

The following diagram illustrates the typical flow of how environment variables are accessed and managed in a Python application.

flowchart TD
    A[Start Application] --> B{Load Environment Variables}
    B --> C[System/Shell Variables]
    B --> D[.env File (if used)]
    C -- Overridden by --> D
    D --> E[Python os.environ]
    E --> F{Application Logic}
    F --> G[Use Config Values]
    G --> H[End Application]

Flowchart illustrating how environment variables are loaded and accessed in a Python application.

Best Practices for Using Environment Variables

To ensure your applications are secure, maintainable, and flexible, follow these best practices when working with environment variables:

1. Separate Configuration from Code

Never hardcode sensitive information or environment-specific settings directly into your source code. Use environment variables for API keys, database URLs, and other credentials.

2. Use Descriptive Names

Name your environment variables clearly and consistently (e.g., DATABASE_URL, API_KEY, DEBUG_MODE). Use uppercase letters and underscores, which is a common convention.

3. Provide Default Values

Always use os.environ.get() with a default value or implement robust error handling for critical variables to prevent application crashes if a variable is missing.

4. Secure Sensitive Data

Ensure .env files are not committed to version control (add them to .gitignore). In production, use secure secrets management services provided by your cloud provider (e.g., AWS Secrets Manager, Azure Key Vault, Google Secret Manager) or orchestration tools (e.g., Kubernetes Secrets).

5. Type Conversion

Environment variables are always strings. Convert them to the appropriate data type (e.g., int(), bool()) in your Python code as needed. For booleans, check for specific string values like 'true' or '1'.