About Computer Directories

You have probably used files and directories on your computer before. However, there are a set of terms that you will hear often, particularly as you work on open science projects or use the command line to manipulate files and directories. Below you will learn about some important terms associated with working with files including working and parent directories.

A directory refers to a folder on a computer that has relationships to other folders. The term “directory” considers the relationship between that folder and the folders within and around it. Directories are hierarchical which means that they can exist within other folders as well as have folders exist within them.

Data Tip: Directory vs Folder: You can think of a directory as a folder. However, the term directory considers the relationship between that folder and the folders within it and around it (it’s full path).

What Is a Parent Directory

The term “parent” directory is used to describe the preceding directory in which a subdirectory is created. A parent directory can have many subdirectories; thus, many subdirectories can share the same parent directory. This also means that parent directories can also be subdirectories of a parent directory above them in the hierarchy.

An example of a directory is your downloads directory. It is the parent directory of any directories or files that get downloaded to your computer or placed within this directory.

In the example below, earth-analytics is the parent directory of both the data and output-plots subdirectories. field-sites is the parent directory for the california directory, etc.

The image files (study-site.jpg and tree-species-distribution-map.jpg) exist within their parent directory: output-plots/spatial-vector directory.

* earth-analytics\
    * data\
        * field-sites\
            * california\
_           * colorado\
              *  streams.csv
    * output-plots\
        * spatial-vector\
            * study-site.jpg
            * tree-species-distribution-map.jpg

What Is the Home Directory?

The home directory on a computer is a directory defined by your operating system. The home directory is the primary directory for your user account on your computer. Your files are by default stored in your home directory.

On Windows, the home directory is typically C:\Users\your-username.

On Mac and Linux, the home directory is typically /home/your-username.

Throughout this textbook, /home/your-username is used as the example home directory and can be considered equivalent to C:\Users\your-username on Windows.

What Is A Working Directory?

While the terminal will open in your home directory by default, you can change the working directory of the terminal to a different location within your computer’s file structure.

The working directory refers to the directory (or location) on your computer that a the tool assumes is the starting place for all paths that you construct or try to access.

For example, when you cd into the earth-analytics directory, it becomes your working directory.

If you run the ls command within the earth-analytics directory (with the contents in the example above):

$ ls

You would see something like this:

data/
output-plots/

The data and output-plots directories are the immediately visible subdirectories within earth-analytics.

By setting your working directory to earth-analytics, you can easily access anything in both of those subdirectories.

Working Directories and Relative vs Absolute Paths in Python

You may be wondering why working directories are important to understand when working with Python (or R or most scientific programming languages).

When set correctly, working directories help the programming language to find files when you create paths.

Within Python, you can define (or set) the working directory of your choice. Then, you can create paths that are relative to that working directory, or create absolute paths, which means they begin at the home directory of your computer and provide the full path to the file that you wish to open.

Relative Paths

A relative path is the path that (as the name sounds) is relative to the working directory location on your computer.

If the working directory is earth-analytics, then Python knows to start looking for your files in the earth-analytics directory.

Following the example above, if you set the working directory to the earth-analytics directory, then the relative path to access streams.csv would be:

data/field-sites/california/colorado/streams.csv

Data Tip The default working directory in any Jupyter Notebook file is the directory in which it is saved. However, you can change the working directory in your code!

However, imagine that you set your working directory to earth-analytics/data which is a subdirectory of earth-analytics.

The correct relative path to the streams.csv file would now look like this:

field-sites/california/colorado/streams.csv

Relative paths are useful if you can count on whoever is running your code to have a working directory setup similar to yours. When the details of your directory setup are shared with others who can replicate it, then you can use relative paths to support reproducibility and collaboration.

Absolute Paths

An absolute path is a path that contains the entire path to the file or directory that you need to access. This path will begin at the home directory of your computer and will end with the file or directory that you wish to access.

/home/your-username/earth-analytics/data/field-sites/california/colorado/streams.csv

Absolute paths ensure that Python can find the exact file on your computer.

However, as you have seen, computers can have a different path constructions, depending on the operating system, and contain usernames that unique to that specific machine.

There are ways to overcome this issue and others associated with finding files on different machines using tools such as the os package in Python. You will learn more about these approaches later in this chapter.