Importing Modules From Subpackages

00:00 A package is just a folder containing one or more Python modules, one of which must be __init__.py. So it’s entirely possible to have the following package structure.

00:11 You have a mypackage/ folder with the three files __init__.py, module1.py, and module2.py. Additionally, you have a subdirectory named mysubpackage/ inside the mypackage/ folder.

00:26 And inside the mysubpackage/ folder is another __init__.py file and a file named module3.py. A package nested inside another package is called a subpackage. In this example, the mysubpackage/ folder is a subpackage of mypackage/ because it contains an __init__.py module as well as a second module called module3.py. Let’s create the structure to see how it works.

00:56 Using your computer’s file explorer or some other tool, create the mysubpackage/ folder on your computer. Make sure you place the folder inside the mypackage/ folder you created earlier.

01:10 In IDLE, open a new editor window and create an __init__.py file that you save in mysubpackage/.

01:24 Then open another file that you save as module3.py, and save it next to the __init__.py in the mypackage/ folder.

01:35 So the place where you store those files is very important for this. In your module3.py file, add the following code. Define a variable named people that equals a list with four strings: ["Christal", "Tappanita, "Martina," "Kate"].

01:59 Save the file and then open the main __init__.py file that’s in the root directory of the package_examples/. That’s the project folder.

02:07 Remove any existing code that is in the main.py file at this moment, and replace it with this code: from mypackage.module1 import greet, and in the next line, from mypackage.mysubpackage.module3 import people. An empty line, and then you loop through the list. for person in people: and on the next line, indented, greet(person).

02:44 The people list from the module3 module inside mysubpackage is imported via the dotted module name mypackage.mysubpackage.module3. Now save and run main.py.

02:59 Cool. The output in the interactive window is Hello, Christal! Hello, Tappanita! Hello, Martina! and Hello, Kate!. And that’s how you can work with subpackages in Python.

03:11 Subpackages are great for organizing code inside very large packages. They help keep the folder structure of a package clean and organized. However, deeply nested subpackages introduce long dotted module names.

03:25 You can imagine how much typing it would take to import a module from a subpackage of a subpackage of a subpackage of a package. So it’s good practice to keep your subpackages at most one or two levels deep.

03:37 And it’s also a good practice to keep video courses on the shorter side, which is a great coincidence because let me look at my notes. There is not that much that I wanted to tell you today about modules and packages, but before we wrap up this course, I have a special treat for you in the next lesson.