In Post #143, we established the need for data persistence by saving our program’s data to files. Before we can write the code to open a file, we first have to answer a simple question: where is the file? Your computer’s file system is like a giant tree of folders and files, and we need to give our program a clear set of directions to find the right one.
These directions are called file paths. Understanding the two main types of paths—absolute and relative—is crucial for writing code that works reliably.
Absolute Paths: The Full Address
An absolute path is the full, complete address of a file or directory, starting from the very top of your file system, which is known as the root directory.
Think of it like a full mailing address for a house: 123 Main Street, Anytown, CA 90210, USA. This address is unambiguous and will point to the same house no matter where you are in the world when you read it.
The key feature of an absolute path is that it always starts from the root. The syntax for the root differs between operating systems.
Syntax on Different Operating Systems
- On Windows: An absolute path starts with a drive letter, like C:\, and uses backslashes as separators.C:\Users\Alice\Documents\project\data.txt
- On macOS and Linux: An absolute path starts with a forward slash /, which represents the root of the file system. It uses forward slashes as separators./home/alice/documents/project/data.txt
Absolute paths are useful when you know the exact, fixed location of a file. However, they are not portable. If you send your code to a friend, their username and folder structure will be different, and a hard-coded absolute path like the ones above will be broken.
Relative Paths: Directions from Here
A relative path describes a file’s location relative to your program’s current working directory (CWD). The CWD is simply the folder you are in when you run your Python script from the terminal.
Think of it like giving directions to a neighbor: “It’s the house next door.” These directions only make sense from a specific starting point.
Relative paths are powerful because they are portable. They don’t start with the root directory.
Common Relative Path Syntax
Let’s imagine your script main.py is in a folder called my_project.
- data.txtThis means “the file data.txt is in the same directory as my script.”
- files/data.txtThis means “look inside a folder named files (which is in the same directory as my script), and find data.txt inside it.”
- ../data.txtThis is a bit more advanced. The .. means “go up one directory level.” This path means “the file data.txt is in the parent directory of where my script is.”
Which One Should You Use?
For most projects, you should almost always prefer relative paths.
By using relative paths for the files within your project folder, you ensure that your project is self-contained. You can zip up the entire project folder, send it to a colleague, move it to a different location on your computer, or upload it to a server, and all the file references will continue to work perfectly because their locations relative to each other have not changed.
Use an absolute path only when you need to refer to a specific, fixed file location on your system that is guaranteed to be outside of your project’s folder structure.
What’s Next?
You now understand the difference between an absolute path (a full, unambiguous address) and a relative path (a portable address relative to your script’s location). This knowledge is essential for preventing the most common error in file handling: the dreaded FileNotFoundError.
Now that we know how to describe where a file is, we are finally ready to learn how to open it. In Post #145, we will learn the modern, safe, and Pythonic way to open and work with files using the with open() statement.
Author
Experienced Cloud & DevOps Engineer with hands-on experience in AWS, GCP, Terraform, Ansible, ELK, Docker, Git, GitLab, Python, PowerShell, Shell, and theoretical knowledge on Azure, Kubernetes & Jenkins. In my free time, I write blogs on ckdbtech.com