Using Python's os Module

30 minutes
  • 2 Learning Objectives

About this Hands-on Lab

Environment variables provide a great way to share information into an application, and being able to read environment variables is a key skill for programming.

You will need basic Python programming and datetime skills for this lab:
– [Certified Associate in Python Programming Certification](https://linuxacademy.com/cp/modules/view/id/470)
– [Python’s os module](https://docs.python.org/3/library/os.html#)

Learning Objectives

Successfully complete this lab by achieving the following learning objectives:

Write Test

Using the best practice, Test-Driven Development, first write a test that will check to make sure your result matches what is wanted. There is a # test section for your code. The test_printer_config.ini file contains the result you should check against. Remember streams and file i/o to read the resulting file, the test file, and assert they are equal.

After you have written the test, run python write_config.py.

This should result in an AssertionError which you will fix in the next step.

import configparser
import os

# data to be used
data_list = [
    ["author", "title", "pages", "due_date", "genre", "isbn"],
    ["Thompson, Keith", "Oh Python! My Python!", 1200, "2020-11-15", "biography", "000-1-000000-00-1"],
    ["Fritts, Larry", "Fun with Django", 150, "2020-06-23", "satire", "00-2-000000-00-2"]
]

novel_text = "Numquam labore labore tempora. Dolore dolorem quisquam aliquam eius dolor non ipsum. Dolorem est velit tempora quaerat. Est magnam porro voluptatem dolore. Adipisci voluptatem consectetur dolore voluptatem voluptatem neque. Adipisci non modi quiquia etincidunt quisquam. Etincidunt consectetur dolore ut. Quaerat ut adipisci sit aliquam quisquam ut. Voluptatem labore porro porro.nnPorro modi numquam non sed dolor. Consectetur dolor adipisci quaerat aliquam adipisci. Etincidunt porro modi dolor neque numquam magnam neque. Ipsum consectetur ut eius ut. Dolor ut modi non est tempora labore sit.nnEtincidunt voluptatem quaerat consectetur sed est etincidunt ipsum. Ut adipisci numquam etincidunt porro porro. Dolore eius modi aliquam. Velit amet sed quaerat etincidunt est. Ut consectetur modi ipsum sed aliquam. Amet tempora quiquia eius voluptatem aliquam dolore ut. Etincidunt dolor non voluptatem eius sed non adipisci."

# instantiate the configparser object
config = configparser.ConfigParser()

# add default section
config["DEFAULT"] = {
    "pub_house": "Atlantic Publishing",
    "number_of_books": '2'
}

# add first book
config["book1"] = {
    "author": data_list[1][0],
    "title": data_list[1][1],
    "genre": data_list[1][4],
    "text": novel_text
}

# add second book
config["book2"] = {
    "author": data_list[2][0],
    "title": data_list[2][1],
    "genre": data_list[2][4],
    "text": novel_text
}

# print to file
with open("printer_config.ini", "w") as f:
    config.write(f)

# test
# student input here
with open("printer_config.ini", "r") as f:
    config_text = f.read()

with open("test_printer_config.ini", "r") as f:
    expected_text = f.read()

assert config_text == expected_text, f"Expected: {expected_text}nnGot: {config_text}"
Change the File So It Has Correct Information

The DEFAULT section of printer_config.ini should look like this:

[DEFAULT]
pub_house = Atlantic Publishing
pub_house_address = 321 Publishers Way, Fargo, ND
pub_house_phone = 555-555-5555

The environment variables are:

  • PUB_HOUSE = "Atlantic Publishing"
  • PUB_HOUSE_ADDRESS = "321 Publishers Way, Fargo, ND"
  • PUB_HOUSE_PHONE = "555-555-5555"

Change the code in write_config.py to update the default section.

import configparser
import os

# data to be used
data_list = [
    ["author", "title", "pages", "due_date", "genre", "isbn"],
    ["Thompson, Keith", "Oh Python! My Python!", 1200, "2020-11-15", "biography", "000-1-000000-00-1"],
    ["Fritts, Larry", "Fun with Django", 150, "2020-06-23", "satire", "00-2-000000-00-2"]
]

novel_text = "Numquam labore labore tempora. Dolore dolorem quisquam aliquam eius dolor non ipsum. Dolorem est velit tempora quaerat. Est magnam porro voluptatem dolore. Adipisci voluptatem consectetur dolore voluptatem voluptatem neque. Adipisci non modi quiquia etincidunt quisquam. Etincidunt consectetur dolore ut. Quaerat ut adipisci sit aliquam quisquam ut. Voluptatem labore porro porro.nnPorro modi numquam non sed dolor. Consectetur dolor adipisci quaerat aliquam adipisci. Etincidunt porro modi dolor neque numquam magnam neque. Ipsum consectetur ut eius ut. Dolor ut modi non est tempora labore sit.nnEtincidunt voluptatem quaerat consectetur sed est etincidunt ipsum. Ut adipisci numquam etincidunt porro porro. Dolore eius modi aliquam. Velit amet sed quaerat etincidunt est. Ut consectetur modi ipsum sed aliquam. Amet tempora quiquia eius voluptatem aliquam dolore ut. Etincidunt dolor non voluptatem eius sed non adipisci."

# instantiate the configparser object
config = configparser.ConfigParser()

# add default section
config["DEFAULT"] = {
    "pub_house": os.getenv("PUB_HOUSE"),
    "pub_house_address": os.getenv("PUB_HOUSE_ADDRESS"),
    "pub_house_phone": os.getenv("PUB_HOUSE_PHONE")
}

# add first book
config["book1"] = {
    "author": data_list[1][0],
    "title": data_list[1][1],
    "genre": data_list[1][4],
    "text": novel_text
}

# add second book
config["book2"] = {
    "author": data_list[2][0],
    "title": data_list[2][1],
    "genre": data_list[2][4],
    "text": novel_text
}

# print to file
with open("printer_config.ini", "w") as f:
    config.write(f)

# test
with open("printer_config.ini", "r") as f:
    config_text = f.read()

with open("test_printer_config.ini", "r") as f:
    expected_text = f.read()

assert config_text == expected_text

Run python write_config.py.

Congrats! You have successfully accessed environment variables using Python’s os module.

Additional Resources

Atlantic Publishing is broken into many divisions. Each division has their own name, address, and phone number. And each division has its own server. The server has environment variables assigned that give the name, address, and phone number of the division.

As an example: pub_house = "Atlantic Publishing" pub_house_address = "321 Publishers Way, Fargo, ND" pub_house_phone = "555-555-5555"

In a previous lab, you created a configuration file that had this information hard-coded. You should update that code to use the environment variables so it does not have to be hard-coded in each division's machine.

Logging In

There are a couple of ways to get in and work with the code. One is to use the credentials provided in the hands-on lab page, log in with SSH, and use a text editor in the terminal.

The other is using VS Code in a web browser. If you'd like to go this route, then you will need to navigate to the public IP address of the workstation server (provided in the hands-on lab page) on port 8080 (example: http://PUBLIC_IP:8080). Your password will be the same password that you'd use to connect over SSH.

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