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Modules

Updated Oct 28, 2019 ·

Overview​

Modules are Python files with a .py extension that contain functions, attributes, and even other modules. Python includes many built-in modules to help us avoid rewriting code.

Common Python Modules​

Python has around 200 built-in modules. Some popular ones:

  • os – Interacts with the operating system, like getting the current directory.
  • collections – Provides advanced data structures.
  • string – Helps with string operations.
  • logging – Logs program events.
  • subprocess – Runs terminal commands from Python.

Importing a Module​

To use a module, we import it with the import keyword.

import os
print(type(os))  # Output: <class 'module'>

Finding Module Functions​

To see what a module offers, check its documentation or use the help function.

import os
help(os)  # Displays a long list of functions and attributes

Using os​

Get Current Directory​

Use os.getcwd() to find the current working directory.

import os
work_dir = os.getcwd()
print(work_dir)

The output is in quotes, which means the output is a string.

'/home/user/projects'

Changing Directory​

Use os.chdir() to move to a different directory.

import os
os.chdir("/home/user/documents")
print(os.getcwd())  # Output: '/home/user/documents'

Module Attributes​

Modules also have attributes, which store values instead of performing actions.

import os
print(os.environ)  # Outputs environment variables as a dictionary

With attributes, we don't need to use "()" as they are not functions. The output is a dictionary:

environ({
  'SHELL': '/bin/bash', 
  'WSL2_GUI_APPS_ENABLED': '1', 
  'WSL_DISTRO_NAME': 'Ubuntu-16.04', 
  'HISTSIZE': '1000000', 
  'PWD': '/mnt/c/project' 
  .....})

Importing a Single Function​

Instead of importing the whole module, we can import only what we need. For example, instead of importing the entire os module, we can only import the specific chdir function.

from os import chdir
chdir("/home/user")

Importing Multiple Functions​

For multiple functions, separate them with commas.

from os import chdir, getcwd
chdir("/home/user/documents")
print(getcwd())  # Output: "/home/user/documents"

Example: Creating a Module​

A module is just a single Python file. Python has built-in modules, but you can also create your own by writing a .py file.

info

Get the script here: Sample python scripts.

This section guides you through creating a Python module for testing network connections.

  1. Install the Requests Module

    • Requests: For sending HTTP requests, handling headers, data, and SSL.
    • Install it using:
    sudo apt install python3-requests

  2. Create the custom_network_module.py Module

    • Code can be found here: Sample python scripts.

    • check_localhost: Verifies if localhost is correctly configured by checking if the IP is 127.0.0.1.

    • check_connectivity: Verifies internet connectivity by sending a GET request.

    • Note that module file names should not contain dashes ("-").

  3. This module can not be used by another script.

    • Create check-disk-cpu-usage.py and use the custom_network_module module.

    • Code can be found here: Sample python scripts.

    • Run code:

      python3  check-disk-cpu-usage.py