How Python Modules & Packages work. Application: Energy

Packages & Modules in Energy

If you’ve been using Python for a while, you’ve probably written import something hundreds of times. Have you ever stopped to think about what exactly you’re importing? Is it a module? A package? Does it matter? Yes, it does matter. And understanding the difference will make you a better Python developer.

Let’s start with the fundamentals.

What is a Module?

A module is simply any .py file. That’s it.

When you create a file called wind.py or solar.py or main.py, you’ve created a module. It doesn’t matter if the file is empty or contains thousands of lines of code. If it ends in .py, it’s a module.

Think of a module as a single book. It contains code (functions, classes, variables) that you can import and use elsewhere. Examples of modules you probably use all the time:

• math - Python’s built-in math module

• random - for generating random numbers

What is a Package?

A package is a folder that contains a special file called __init__.py along with one or more modules.

The __init__.py file is what transforms an ordinary directory into a package. This file can be empty (and often is for beginners), but its presence tells Python: “Treat this folder as a package that can be imported.”

Think of a package as a library building that contains multiple books (modules) organized together. Examples of popular packages:

• pandas - for data analysis

• numpy - for numerical computing

• pvlib - for solar photovoltaic system modeling (we’ll use this later)

What is a Directory?

A directory is simply a folder without the __init__.py file. You can import directories. They become what are called “namespace packages” or “implicit namespace packages.” So import directory_energy works just fine.

The difference between a package and a directory is the presence of __init__.py. Add the file, and you get a Python package. Remove it, and you get a namespace package (a directory) that’s just a container.

Installing Packages in PyCharm

Quick tip for PyCharm users on macOS, to install a package like pvlib:

1. Go to PyCharm menu → Settings

2. Navigate to Python → Interpreter

3. Click the + button

4. Search for the package (e.g., pvlib)

5. Click Install Package

Creating Packages and Modules in PyCharm

In PyCharm, when you click the + button in the Project view:

• Python Package : Creates a folder with __init__.py

• Python File : Creates a module (.py file)

• Directory : Creates a plain folder (no __init__.py)

What you can do with __init__.py

Full code below with the Python model.

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