Python os module

Filed Under: Python

Python OS module provides easy functions that allow us to interact and get Operating System related information and even control processes up to a limit.

Python OS Module

The functions OS module provides allows us to operate on underlying Operating System tasks, irrespective of it being a Windows Platform, Macintosh or Linux. In this lesson, we will review these functions and what we can do with these.

Let us start our journey with these functions and what information they offer.

Python import os

Please note that first of all we have to import OS module in our program, then only we can execute any of it’s functions.

python os import, python os module

os.name

This function gives the name of the OS module it imports. This differs based on the underlying Operating System. Currently, it registers ‘posix’, ‘os2’, ‘ce’, ‘nt’, ‘riscos’ and ‘java’.

Let’s execute this on the system:


>>> print(os.name)
posix

Clearly, this can output different platforms based on the interpreter.

os.environ

environ is not a function but a process parameter through which we can access environment variables of the system.
Let’s see sample code snippet:


import os
output = os.environ['HOME']
print(output)

When we run this script, the following will be the output:
python os environment variable

We can use it to work with the environment variables, read more at Python set environment variable.

os.execvp

execvp function is one of the ways to run other commands on the system.
Let’s see sample code snippet for this function:


import os
program = "python"
arguments = ["hello.py"]
print(os.execvp(program, (program,) +  tuple(arguments)))

For this, we just created a sample script as hello.py with following code:


print('Hello')

When we run this script, the following will be the output:
python os module, python os execute other script

os.getuid

This os module function returns current process’s user ID or UID, as it is populary known.


>>> os.getuid()
501

So, the current shell process ID is 501.

os.rename

With the python os rename function, we can easily rename a file.


import os
fileDir = "JournalDev.txt"
os.rename(fd,'JournalDev_Hi.txt')

Note that for this, we must provide correct permissions to our script.

os.system

Python os system function allows us to run a command in the Python script, just like if I was running it in my shell. For example:


import os
currentFiles = os.system("users > users.txt")

When I ran this script, a new file was made in the same directory with name users.txt and content String as ‘shubham’ as this is returned by original shell as well:
Python OS System command

Note that this is a very powerful command and should be used cautiously.

os.error

Now, errors in any program are inevitable. Python provides us a function error which allows to to show OS level erros, apart from normal Python specific errors. See this in action with this snippet:


import os

try:
    # If the file does not exist or we dont have,
    # then it would throw an IOError
    filename = 'JournalDevsas.txt'
    jdFile = open(filename, 'rU')
    text = jdFile.read()
    jdFile.close()

# Control jumps here if of the above statement throws IOError.
except IOError:
    # Below statement logs <class 'OSError'>
    print(os.error)

    # In any case, the code will continue
    # after it logs the error.

os.getpid

This function returns current process ID or PID, as it is populary known.


>>> os.getpid()
71622

So, the current shell process’s user ID is 71622.

os.listdir

This function just lists out the files and directories present in the current working directory.


>>> import os
>>> os.listdir()
['.DS_Store', '.localized', 'JournalDev', 'Java', 'Python']

It returns an iterable list of directory and file names.

os.uname

This function return information which identifies current Operating System on which this is executed.


>>> os.uname()
posix.uname_result(sysname='Darwin', nodename='Shubham.local', release='17.2.0', version='Darwin Kernel Version 17.2.0: Fri Sep 29 18:27:05 PDT 2017; root:xnu-4570.20.62~3/RELEASE_X86_64', machine='x86_64')

That was prettry detailed actually.

import os.path vs import os

os.path works strangely actually. It looks like os packaged with a submodule path but actually, os is a normal module which operate with sys.module to support os.path. Let us list what happens behind the scenes:

  • When Python starts, it loads many modules into sys.module.
  • os module is also loaded when Python starts. It assigns its path to the os specific module attribute.
  • It injects sys.modules['os.path'] = path so that you’re able to do import os.path as though it was a submodule.

Summary

In this lesson, we read about various functions provided by OS module in Python and saw how they work. See more lessons on Python here.

Reference: API Doc

Comments

  1. Vishwas Narayan says:

    we need something more as the students as new to this compiler

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