The os Module

Introduction

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

Syntax

  • import os

Parameters

ParameterDetails
PathA path to a file. The path separator may be determined by os.path.sep.
ModeThe desired permission, in octal (e.g. 0700)

Change permissions on a file

os.chmod(path, mode)

where mode is the desired permission, in octal.

Create a directory

os.mkdir('newdir')

If you need to specify permissions, you can use the optional mode argument:

os.mkdir('newdir', mode=0700)

Determine the name of the operating system

The os module provides an interface to determine what type of operating system the code is currently running on.

os.name

This can return one of the following in Python 3:

  • posix
  • nt
  • ce
  • java

More detailed information can be retrieved from sys.platform

Sometimes you need to determine the target of a symlink. os.readlink will do this:

print(os.readlink(path_to_symlink))

Get current directory

Use the os.getcwd() function:

print(os.getcwd())

makedirs - recursive directory creation

Given a local directory with the following contents:

 └── dir1
     ├── subdir1
     └── subdir2

We want to create the same subdir1, subdir2 under a new directory dir2, which does not exist yet.

import os

os.makedirs("./dir2/subdir1")
os.makedirs("./dir2/subdir2")

Running this results in

├── dir1
│   ├── subdir1
│   └── subdir2
└── dir2
    ├── subdir1
    └── subdir2

dir2 is only created the first time it is needed, for subdir1's creation.

If we had used os.mkdir instead, we would have had an exception because dir2 would not have existed yet.

    os.mkdir("./dir2/subdir1")
OSError: [Errno 2] No such file or directory: './dir2/subdir1'

os.makedirs won't like it if the target directory exists already. If we re-run it again:

OSError: [Errno 17] File exists: './dir2/subdir1'

However, this could easily be fixed by catching the exception and checking that the directory has been created.

try:
    os.makedirs("./dir2/subdir1")
except OSError:
    if not os.path.isdir("./dir2/subdir1"):
        raise

try:
    os.makedirs("./dir2/subdir2")
except OSError:
    if not os.path.isdir("./dir2/subdir2"):
        raise

Remove a directory

Remove the directory at path:

os.rmdir(path)

You should not use os.remove() to remove a directory. That function is for files and using it on directories will result in an OSError