How Imports Work in Python

And a bit about packages

Photo by Blanca Paloma Sánchez on Unsplash

The Python import system is pretty straightforward... to a point. Importing code present in the same directory you’re working in is very different from importing between multiple files present in multiple directories. Through this post, I analyse some scenarios commonly encountered when working with imports, hopefully making it easier for you to create your own packages.

Table of Contents

An Example
What Happens When You Import a Python File?
Terminology
Import Scenarios
Analysis
Building a Package
The Syntax of Your Import Statement
Notes and Resources

An Example

We’ll start with a simple example and build on it throughout the post. Let’s say we have two simple Python files in a directory called PythonImportExample.

Our example — by author using draw.io

PythonImportExample/
    file1.py
    file2.py

Let’s say file1.py contains the following:

print("This is file1.py")

And file2.py imports file1.py.

import file1
print("This is file2.py")

The import looks something like this:

file1.py getting imported into file2.py — by author using draw.io

What Happens When You Import a Python File?

When a Python file is imported, it is executed, and then added to the namespace of the file importing it.

For example, when file2.py is executed, we get the following output:

$ cd PythonImportExample
$ python file2.py
This is file1.py
This is file2.py

The imported file is executed right before its imported. So if we put the import statement in file2.py below the print statement like so:

print("This is file2.py")
import file1