Python OS Module

This module provides a portable way of using operating system dependent functionality.

Pathlib vs OS Module

The pathlib module provides a lot more functionality than the ones listed here, like getting file name, getting file extension, reading/writing a file without manually opening it, etc. See the official documentation if you intend to know more.
For a more in-depth look at both, see the File and directory Paths page.

Linux and Windows Paths

On Windows, paths are written using backslashes (\) as the separator between folder names. On Unix based operating system such as macOS, Linux, and BSDs, the forward slash (/) is used as the path separator. Joining paths can be a headache if your code needs to work on different platforms.

Fortunately, Python provides us with os.path.join to handle this.

import os

# Join path components using the correct separator for the OS
os.path.join('usr', 'bin', 'spam')

usr\bin\spam

Joining paths is helpful if you need to create different file paths under the same directory.

my_files = ['accounts.txt', 'details.csv', 'invite.docx']

# Join each filename with the base directory
for filename in my_files:
    print(os.path.join('/home/labex/project', filename))

/home/labex/project/accounts.txt
/home/labex/project/details.csv
/home/labex/project/invite.docx

The current working directory

import os

# Get the current working directory
os.getcwd()

/home/labex/project

# Change the current working directory
os.chdir('/usr/bin')

# Verify the change
os.getcwd()

/usr/bin

Creating new folders

import os
# Create directories recursively (creates all parent directories if needed)
os.makedirs('/tmp/delicious/walnut/waffles')

Absolute vs. Relative paths

There are two ways to specify a file path.

An absolute path, which always begins with the root folder
A relative path, which is relative to the program’s current working directory

There are also the dot (.) and dot-dot (..) folders. These are not real folders, but special names that can be used in a path. A single period (“dot”) for a folder name is shorthand for “this directory.” Two periods (“dot-dot”) means “the parent folder.”

Handling Absolute paths

To see if a path is an absolute path:

import os
# Check if path is absolute (starts with root)
os.path.isabs('/')

True

# Relative paths return False
os.path.isabs('..')

False

You can also extract an absolute path:

import os
# Get current directory first
os.getcwd()

/home/labex/project

# Convert relative path to absolute path
os.path.abspath('..')

/home

Handling Relative paths

You can get a relative path from a starting path to another path.

import os
# Get relative path from start path to target path
os.path.relpath('/etc/passwd', '/')

etc/passwd

Path and File validity

Checking if a file/directory exists

import os

# Check if path exists (file or directory)
os.path.exists('.')

True

os.path.exists('setup.py')

True

os.path.exists('/etc')

True

os.path.exists('nonexistentfile')

False

Checking if a path is a file

import os

# Check if path is a file
os.path.isfile('setup.py')

True

os.path.isfile('/home')

False

os.path.isfile('nonexistentfile')

False

Checking if a path is a directory

import os

# Check if path is a directory
os.path.isdir('/')

True

os.path.isdir('setup.py')

False

os.path.isdir('/spam')

False

Getting a file’s size in bytes

import os

# Get file size in bytes
os.path.getsize('/usr/bin/python3')

Listing directories

import os

# List all files and directories in the specified path
os.listdir('/usr/bin')

['0409', '12520437.cpx', '12520850.cpx', '5U877.ax', 'aaclient.dll',
--snip--
'xwtpdui.dll', 'xwtpw32.dll', 'zh-CN', 'zh-HK', 'zh-TW', 'zipfldr.dll']

Directory file sizes

WARNING

Directories themselves also have a size! So, you might want to check for whether a path is a file or directory using the methods in the methods discussed in the above section.

import os
total_size = 0

# Calculate total size of all files in directory
for filename in os.listdir('/usr/bin'):
    # Join directory path with filename and get size
    total_size = total_size + os.path.getsize(os.path.join('/usr/bin', filename))
print(total_size)

1117846456

Deleting files and folders

Calling os.unlink(path) will delete the file at path.
Calling os.rmdir(path) will delete the folder at path. This folder must be empty of any files or folders.

Walking a Directory Tree

import os

# Walk through directory tree recursively
for folder_name, subfolders, filenames in os.walk('/tmp/delicious'):
    print(f'The current folder is {folder_name}')
    # Iterate through subdirectories
    for subfolder in subfolders:
        print(f'SUBFOLDER OF {folder_name}: {subfolder}')
    # Iterate through files
    for filename in filenames:
        print(f'FILE INSIDE {folder_name}: filename{filename}')
    print('')

The current folder is /tmp/delicious
SUBFOLDER OF /tmp/delicious: cats
SUBFOLDER OF /tmp/delicious: walnut
FILE INSIDE /tmp/delicious: spam.txt

The current folder is /tmp/delicious/cats
FILE INSIDE /tmp/delicious/cats: catnames.txt
FILE INSIDE /tmp/delicious/cats: zophie.jpg

The current folder is /tmp/delicious/walnut
SUBFOLDER OF /tmp/delicious/walnut: waffles

The current folder is /tmp/delicious/walnut/waffles
FILE INSIDE /tmp/delicious/walnut/waffles: butter.txt