1. Create a Virtual Environment

python3 -m venv venv

I’m on macOS; Windows users should adapt commands accordingly.

2. Activate the Environment

source venv/bin/activate

Again, adjust for Windows if needed.

3. Reading Environment Variables in Python

Use the os module:

import os

all_env = os.environ            # dictionary-like object
path = os.environ.get("PATH")   # fetch a specific key

4. Temporary Variables from the Shell

export TEST_PATH="Hello World"

This works only for the current shell session.

5. Making Variables Persistent in the Virtualenv

Edit venv/bin/activate and add:

ABC="hello_world !"
export ABC

After modifying the file, deactivate and reactivate your virtual environment so the new settings take effect.

6. Real-World Example: Boto3 Credentials

Hard-coding AWS keys in source code is a security risk. Instead, store them as environment variables:

import os
import boto3

AWS_KEY_ID = os.environ.get("AWS_KEY_ID")
AWS_SECRET_KEY = os.environ.get("AWS_SECRET_KEY")

s3 = boto3.client(
    "s3",
    region_name="ap-northeast-2",
    aws_access_key_id=AWS_KEY_ID,
    aws_secret_access_key=AWS_SECRET_KEY,
)

print(s3.list_buckets())

This keeps your credentials out of version control while making your scripts clean and shareable.***