How to Set Environment Variables in Python

1. What are Environment Variables?

In computers, environment variables are settings that store information necessary for the operating system or application to run. These can be paths, such as the path to the Python interpreter, or specific values, such as the location of a configuration file. Setting environment variables in Python is an important technique that helps us better manage the various configurations required for program execution.

2. How to Set Environment Variables

Python provides several methods for setting environment variables, and you can choose the method that suits your needs.

2.1 Setting Environment Variables Using the os Module

Python’s built-in module os provides several functions for managing operating system functionality, including setting and getting environment variables. The following example uses the os module to set environment variables:

import os

# Setting an environment variable
os.environ['MY_ENV_VAR'] = 'Hello, World!'

# Getting an environment variable
my_var = os.environ.get('MY_ENV_VAR')
print(my_var) # Output: Hello, World!

In this example, we set the environment variable MY_ENV_VAR to Hello, World! using os.environ['MY_ENV_VAR']. Then, use os.environ.get('MY_ENV_VAR') to retrieve the value of the environment variable and print it out.

2.2 Setting Environment Variables Using the Python-dotenv Library

Python-dotenv is a third-party library that can load environment variables from a .env file. It supports importing environment variables from a .env file and injecting them into the Python runtime environment. The following is example code for setting environment variables using the Python-dotenv library:

First, install the Python-dotenv library:

pip install python-dotenv

<p>Then, create a file named <code>.env in the project root directory with the following format:

MY_ENV_VAR=Hello, World!


Next, load and use these environment variables using the following code:
from dotenv import load_dotenv

# Load environment variables from the .env file
load_dotenv()

# Get environment variables
my_var = os.environ.get('MY_ENV_VAR')
print(my_var) # Output: Hello, World!

In this example, we import the Python-dotenv library using from dotenv import load_dotenv and use the load_dotenv() function to load the environment variables from the .env file. We then use os.environ.get('MY_ENV_VAR') to get the value of the environment variable and print it.
2.3 Using virtualenv Virtual Environments
In Python, virtual environments are a way to isolate the dependencies and environments required for Python project development. A virtual environment allows you to run multiple Python projects simultaneously on the same machine, each with its own independent environment and package dependencies. When you install Python packages in a virtual environment, they only take effect in the current virtual environment and do not affect the global Python environment. 
The following is example code for creating and activating a virtual environment using virtualenv:
First, you need to install virtualenv:
pip install virtualenv

Then, create a virtual environment named myenv with the following code:
virtualenv myenv

Next, you can activate the virtual environment with the following code:

On Windows:

myenvScriptsactivate


On Mac/Linux:

source myenv/bin/activate

After activating a virtual environment, we can install required Python packages without affecting the global Python environment. We can also set and use environment variables within the virtual environment, for example:
export MY_ENV_VAR=Hello, World!

While this method doesn't directly set Python environment variables, it can still meet the needs of projects that require setting environment variables.
3. Summary
This article introduced three methods for setting environment variables in Python: using the os module, the Python-dotenv library, and the virtualenv virtual environment. You can choose the appropriate method to set and use environment variables based on your project's needs. Environment variables, as configuration information required for program execution, allow you to flexibly adjust program behavior without modifying the code. Mastering the methods for setting environment variables can help you better manage and use Python programs.