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This section provides detailed insights into the boilerplate script for writing custom applications, and includes an in-depth explanation of the built-in functions within the pplapp module. Additionally, examples of third-party applications are provided to demonstrate the versatility and practical applications of the pplapp module.

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Write Application from Boilerplate

The boilerplate script provided by Direct Energy Partners helps establish the NATS connection and allows you to write your own applications to manage power and energy resources. To create your custom application, start with this boilerplate script. Add your logic to the pms() function defined in the script, then run the application.
boilerplate.py
import time
from pplapp import Pplapp
from dotenv import load_dotenv
import os

# Load environment variables from .env file
load_dotenv()

# Constants:
startupDelay = 5
executionDelay = 5

# Main function:
def pms(app):
    pass

# Helper functions:
def function1():
    pass

def function2():
    pass

def function3():
    pass

# Main code that will create a NATS connection and run the PMS loop
def main():
    try:
        # Define the IP address of the controller, and username and password for the NATS connection
        ipAddress = "192.168.1.10"
        username = os.getenv("NATS_USERNAME")
        password = os.getenv("NATS_PASSWORD")

        if not username or not password:
            raise ValueError("NATS username or password not set in environment variables")

        # Initialize the NATS connection to the controller
        app = Pplapp(ipAddress, username, password)

        time.sleep(startupDelay)

        # Run the PMS loop
        while True:
            pms(app)
            time.sleep(executionDelay)

    except Exception as e:
        print(f"Failed to initialize PMS: {e}")

    except KeyboardInterrupt:
        print("Exiting program")
        app.connectToNats = False

if __name__ == "__main__":
    main()
Detailed Steps Below is a step-by-step explanation of what the boilerplate script, as shown previously, does:
1

Importing Required Modules

  • The script begins by importing necessary modules:
    • time for handling delays.
    • pplapp for creating the NATS interface with the controller.
    • dotenv for loading environment variables from a .env file.
    • os for accessing environment variables and interacting with the operating system.
2

Load Environment Variables

  • The script loads environment variables from a .env file.
  • This is used for loading credentials, such as the username and password, required for establishing the NATS client connection.
3

Define Constants

  • Define startupDelay and executionDelay variables to control the delay for startup and subsequent executions of the main loop.
  • Additional constants for use in the pms() function can also be added here.
4

Main PMS Function

  • Define a function named pms(). This function currently contains no logic but is where you will write your custom application or function.
5

Helper Functions

  • Helper functions can be defined here. A Python helper function is a small, auxiliary function designed to perform a specific, often repetitive task to support the main function and improve code modularity and readability.
6

Initialization and Main Loop

  • IP Address and Credentials Assignment:
    • Assign the IP address of the controller that the custom application will interface with, as this address is essential for establishing a connection.
    • Additionally, set up the username and password for the NATS connection to ensure secure access and authentication. The username and password are loaded from the .env file.
  • Connecting to NATS Server: Use the pplapp module, initialized with the assigned IP address, to connect to the NATS server.
  • Running the Script:
    • Implement a while loop that runs indefinitely, allowing continuous reception of data and sending of control commands.
    • Within this loop, call the pms() function to execute your custom logic.
    • Adjust the interval between executions as needed by modifying the executionDelay variable.
  • The main loop should be enclosed within a try-except block to catch and handle any errors that occur during execution.
7

Exception Handling

By incorporating a try-except block, you make your script more robust and reliable, as it can manage errors effectively and respond to user interruptions in a user-friendly way.
  • General Exceptions: Handle a broad range of unexpected errors. Use this to catch and manage errors that don’t fall into specific categories.
  • Keyboard Interrupts: Handle user interruptions gracefully, ensuring that the script exits in a controlled manner.
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