• Discuss the basic directory structure of a CLI.
• Outline the first steps in building a CLI.

You now have a basic idea of what constitutes a CLI. Fork and clone this lesson for a project template for your CLI.

Take a look at the directory structure:

.
├── Pipfile
├── Pipfile.lock
├── README.md
└── lib
    ├── models
    │   ├── __init__.py
    │   └── model_1.py
    ├── cli.py
    ├── debug.py
    └── helpers.py

Note: The directory also includes two files named CONTRIBUTING.md and LICENSE.md that are specific to Flatiron's curriculum. You can disregard or delete the files if you want.

You might have noticed in the file structure- there's already a Pipfile!

Install any additional dependencies you know you'll need for your project by adding them to the Pipfile. Then run the commands:

pipenv install
pipenv shell

A CLI is, simply put, an interactive script and prompts the user and performs operations based on user input.

The project template has a sample CLI in lib/cli.py that looks like this:

# lib/cli.py

from helpers import (
    exit_program,
    helper_1
)


def main():
    while True:
        menu()
        choice = input("> ")
        if choice == "0":
            exit_program()
        elif choice == "1":
            helper_1()
        else:
            print("Invalid choice")


def menu():
    print("Please select an option:")
    print("0. Exit the program")
    print("1. Some useful function")


if __name__ == "__main__":
    main()

The helper functions are located in lib/helpers.py:

# lib/helpers.py

def helper_1():
    print("Performing useful function#1.")


def exit_program():
    print("Goodbye!")
    exit()

You can run the template CLI with python lib/cli.py, or include the shebang and make it executable with chmod +x. The template CLI will ask for input, do some work, and accomplish some sort of task.

Past that, CLIs can be whatever you'd like, as long as you follow the project requirements.

Of course, you will update lib/cli.py with prompts that are appropriate for your application, and you will update lib/helpers.py to replace helper_1() with a useful function based on the specific problem domain you decide to implement, along with adding other helper functions to the module.

In the lib/models folder, you should rename model_1.py with the name of a data model class from your specific problem domain, and add other classes to the folder as needed. The file lib/models/__init__.py has been initialized to create the necessary database constants. You need to add import statements to the various data model classes in order to use the database constants.

You are also welcome to implement a different module and directory structure. However, your project should be well organized, modular, and follow the design principal of separation of concerns, which means you should separate code related to:

• User interface
• Data persistence
• Problem domain rules and logic

README.md is a Markdown file that should describe your project. You will replace the contents of this README.md file with a description of your actual project.

Markdown is not a language that we cover in Flatiron's Software Engineering curriculum, but it's not a particularly difficult language to learn (if you've ever left a comment on Reddit, you might already know the basics). Refer to the cheat sheet in this assignments's resources for a basic guide to Markdown.

This README serves as a template. Replace the contents of this file to describe the important files in your project and describe what they do. Each Python file that you edit should get at least a paragraph, and each function should be described with a sentence or two.

Describe your actual CLI script first, and with a good level of detail. The rest should be ordered by importance to the user. (Probably functions next, then models.)

Screenshots and links to resources that you used throughout are also useful to users and collaborators, but a little more syntactically complicated. Only add these in if you're feeling comfortable with Markdown.

A lot of work goes into a good CLI, but it all relies on concepts that you've practiced quite a bit by now. Hopefully this template and guide will get you off to a good start with your Phase 3 Project.

Happy coding!

• Markdown Cheat Sheet