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.

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

>>> 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']

>>> for filename in my_files:
...     print(os.path.join('C:\\Users\\asweigart', filename))
...
# C:\Users\docs\accounts.txt
# C:\Users\docs\details.csv
# C:\Users\docs\invite.docx

The current working directory

>>> import os

>>> os.getcwd()
# 'C:\\Python34'
>>> os.chdir('C:\\Windows\\System32')

>>> os.getcwd()
# 'C:\\Windows\\System32'

Creating new folders

>>> import os
>>> os.makedirs('C:\\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
>>> os.path.isabs('/')
# True

>>> os.path.isabs('..')
# False

You can also extract an absolute path:

>>> import os
>>> os.getcwd()
'/home/docs'

>>> os.path.abspath('..')
'/home'

Handling Relative paths

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

>>> import os
>>> os.path.relpath('/etc/passwd', '/')
# 'etc/passwd'

Path and File validity

Checking if a file/directory exists

>>> import os

>>> 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

>>> 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

>>> os.path.isdir('/')
# True

>>> os.path.isdir('setup.py')
# False

>>> os.path.isdir('/spam')
# False

Getting a file’s size in bytes

>>> import os

>>> os.path.getsize('C:\\Windows\\System32\\calc.exe')
# 776192

Listing directories

>>> import os

>>> os.listdir('C:\\Windows\\System32')
# ['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

>>> for filename in os.listdir('C:\\Windows\\System32'):
...     total_size = total_size + os.path.getsize(os.path.join('C:\\Windows\\System32', 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
>>>
>>> for folder_name, subfolders, filenames in os.walk('C:\\delicious'):
...     print(f'The current folder is {folder_name}')
...     for subfolder in subfolders:
...         print(f'SUBFOLDER OF {folder_name}: {subfolder}')
...     for filename in filenames:
...         print(f'FILE INSIDE {folder_name}: filename{filename}')
...     print('')
...
# The current folder is C:\delicious
# SUBFOLDER OF C:\delicious: cats
# SUBFOLDER OF C:\delicious: walnut
# FILE INSIDE C:\delicious: spam.txt

# The current folder is C:\delicious\cats
# FILE INSIDE C:\delicious\cats: catnames.txt
# FILE INSIDE C:\delicious\cats: zophie.jpg

# The current folder is C:\delicious\walnut
# SUBFOLDER OF C:\delicious\walnut: waffles

# The current folder is C:\delicious\walnut\waffles
# FILE INSIDE C:\delicious\walnut\waffles: butter.txt