09_env_variables.py

"""
Module 09: Environment Variables and dotenv
Learn: os.getenv(), .env files, python-dotenv

In the advanced courses, EVERY project starts with:
    from dotenv import load_dotenv
    load_dotenv()
    DEFAULT_MODEL = os.getenv("DEFAULT_MODEL", "gpt-4o-mini")
"""

import os

# --- os.getenv() — read environment variables ---
# Returns None if not set, or a default value
home = os.getenv("HOME")
print(f"Home directory: {home}")

# With a default (the pattern used in all courses)
model = os.getenv("DEFAULT_MODEL", "gemini/gemini-2.0-flash")
print(f"Model: {model}")

db_path = os.getenv("DB_PATH", "ecommerce.db")
print(f"Database: {db_path}")

# --- Why .env files? ---
# You don't want API keys in your code!
# Bad:  OPENAI_API_KEY = "sk-abc123..."
# Good: OPENAI_API_KEY is in .env file, loaded at runtime

# --- python-dotenv ---
# Create a sample .env file to demonstrate
from pathlib import Path

env_content = """# Sample .env file
DEFAULT_MODEL=gemini/gemini-2.0-flash
EMBEDDING_MODEL=google/text-embedding-004
APP_NAME=Green Bites AI
"""
Path(".env.demo").write_text(env_content)

# Load it (in real projects, this is just .env)
from dotenv import load_dotenv

load_dotenv(".env.demo")

# Now these are available via os.getenv
app_name = os.getenv("APP_NAME", "Unknown")
embedding = os.getenv("EMBEDDING_MODEL", "default")
print(f"\nLoaded from .env.demo:")
print(f"  APP_NAME: {app_name}")
print(f"  EMBEDDING_MODEL: {embedding}")

# --- os.environ (the full dictionary) ---
# You can also access all env vars as a dict
# print(dict(os.environ))  # Warning: prints everything!

# Cleanup
if os.path.exists(".env.demo"):
    os.remove(".env.demo")

# 🎯 Exercise: Create a .env file with YOUR_NAME=... and load it