## Loading Environment Variables Let's learn about loading environment variables in a Python project. We'll use a file called `.env` to store sensitive information like our private key and address for the project. **1. Create a `.env` file** Create a `.env` file in your project directory, and we'll add our sensitive data here. ``` MY_ADDRESS="0xf39f0d6e51aad88f6f4c6eba88827279cfffb92266" PRIVATE_KEY="0xac0974bec39a17e36ba4a6bd4d238ff1944bacb478cbded5efcae784d7f4f2ff80" RPC_URL="http://127.0.0.1:8545" ``` **2. Install the `python-dotenv` package** We can use the `python-dotenv` package to load our environment variables. We'll use the terminal to install this package. ```bash uv add python-dotenv ``` **3. Import the necessary libraries and functions** We'll import the `load_dotenv` function from `python-dotenv`, and the `os` module. ```python from dotenv import load_dotenv import os ``` **4. Load the environment variables** We can load the environment variables using the `load_dotenv` function. ```python load_dotenv() ``` **5. Access environment variables** Once the environment variables are loaded, we can access them using the `os.getenv()` function. ```python RPC_URL = os.getenv("RPC_URL") MY_ADDRESS = os.getenv("MY_ADDRESS") PRIVATE_KEY = os.getenv("PRIVATE_KEY") ``` **6. Add the `.env` file to your `.gitignore` file** It's very important to include the `.env` file in your `.gitignore` file. This will ensure that the file is not committed to your version control system, preventing accidental exposure of your sensitive information. **7. Rename your project file** Rename your project file to reflect that you're working with sensitive information, we'll add _unsafe_ to our file name. ```python # original file deploy_favorites.py # new file deploy_favorites_unsafe.py ``` **8. Never use a private key associated with real funds in a `.env` file** Using a private key associated with real funds in a `.env` file is a major security risk and should never be done! Instead, use a separate file or configuration that is not part of your project's source control. **9. What to do instead of `.env`** Instead of using a `.env` file, a better approach is to utilize a separate configuration file or a dedicated environment variable management system that is designed for security. This is especially crucial when handling sensitive data like private keys. **10. Example Code** ```python from web3 import Web3 from vyper import compile_code from dotenv import load_dotenv import os load_dotenv() RPC_URL = os.getenv("RPC_URL") MY_ADDRESS = os.getenv("MY_ADDRESS") PRIVATE_KEY = os.getenv("PRIVATE_KEY") def main(): print("Let's read in the Vyper code and deploy it!") with open("favorites.vy", "r") as favorites_file: favorites_code = favorites_file.read() compilation_details = compile_code(favorites_code, output_formats=["bytecode", "abi"]) print(compilation_details) w3 = Web3(Web3.HTTPProvider(RPC_URL)) favorites_contract = w3.eth.contract(bytecode=compilation_details["bytecode"], abi=compilation_details["abi"]) # To deploy, we must build a transaction print("Building the transaction...") nonce = w3.eth.get_transaction_count(MY_ADDRESS) transaction = favorites_contract.constructor().build_transaction({ "nonce": nonce, "from": MY_ADDRESS, "gasPrice": w3.eth.gas_price }) signed_transaction = w3.eth.account.sign_transaction(transaction, PRIVATE_KEY) # We use the Web3 sendRawTransaction function to send the signed transaction to the blockchain w3.eth.send_raw_transaction(signed_transaction.rawTransaction) print("Deployed! Transaction Hash:", signed_transaction.hash) ```