Tutorial 3: Modulized OS Information

In this tutorial, we will introduce a way to organize more complex code. Code will be organzied in modules.

Terms

Before we goes deep into the code, let’s clearify some concepts of terms.

• Package
  • A collection of libs that organized for a kind of purpose
  • Package is distributed and can be installed
• Lib
  • A collection of modules that are organized under a folder
• Module
  • A collection of classes, functions, variables defined in a file
  • Every file is a module
  • Module can be imported, reloaded and the variable and function can be used

OS Info Module

Let’s create a simple lib called os_info, which contains a module called info.py.

In the %{ROOT} dir, create a folder called ‘modulized_os_information’

~$ mkdir os_info
~$ cd os_info
~$ touch info.py

Now we have created the lib and a module. Put the code what we previous generaged in the last tutorialTutorial 1: Environment Setup.

#!/usr/bin/env python
# -*- encoding: utf-8 -*-
# Author: Will<willji@outlook.com>
# Created on 2018-01-10 19:49:12

import os
from collections import defaultdict

def get_os_info():

    command = os.popen('lsb_release -a')
    results = command.readlines()

    lsb_dict = defaultdict()

    for result in results:
        (d_type, d_value) = result.split(':\t')
        lsb_dict[d_type.strip()] = d_value.strip()

    return lsb_dict


def display_os_info(lsb_dict):
    # print lsb_dict
    for key in lsb_dict:
        print '{} \t -- \t : {}'.format(key, lsb_dict[key])

if __name__ == '__main__':
    values = get_os_info()
    display_os_info(values)

We can test the python code in the sub folder and see the result:

~$ python info.py
Release          --      : 16.04
Codename         --      : xenial
Distributor ID   --      : Ubuntu
Description      --      : Ubuntu 16.04.3 LTS

Use the module

After the module created, we can used it now.

~$ code test_info.py

and the code should looks like:

#!/usr/bin/env python
# -*- encoding: utf-8 -*-
# Author: Will<willji@outlook.com>
# Created on 2018-01-11 11:18:12

import info

values = info.get_os_info()
info.display_os_info(values)

and run the code:

~$ python test_info.py
Release          --      : 16.04
Codename         --      : xenial
Distributor ID   --      : Ubuntu
Description      --      : Ubuntu 16.04.3 LTS

Import will run the code from the module, the first time imported.

~$ code test_test_info.py

with the code:

#!/usr/bin/env python
# -*- encoding: utf-8 -*-
# Author: Will<willji@outlook.com>
# Created on 2018-01-11 11:18:12

import test_info

import test_info

$ python test_test_info.py
Release          --      : 16.04
Codename         --      : xenial
Distributor ID   --      : Ubuntu
Description      --      : Ubuntu 16.04.3 LTS

The test_info.py is excuted the first time imported.

Every thing goes well, we got what we expected.

But it is too simple, maybe too naive?

Organize modules

In most cases the modules are organized in a lib folder, and called from outside of the folder.

Let’s try:

~$ cd ..
~$ code modulized_os_info.py

and the code is:

#!/usr/bin/env python
# -*- encoding: utf-8 -*-
# Author: Will<willji@outlook.com>
# Created on 2018-01-10 19:49:12

from os_info import info

values = info.get_os_info()
info.display_os_info(values)

Let’s have a test:

$ python modulized_os_info.py
Traceback (most recent call last):
  File "modulized_os_info.py", line 7, in <module>
    from os_info import info
ImportError: No module named os_info

The module is not existed.

The fix is quite simple:

~$ touch os_info/__init__.py

Now try again:

$ python modulized_os_info.py
Release          --      : 16.04
Codename         --      : xenial
Distributor ID   --      : Ubuntu
Description      --      : Ubuntu 16.04.3 LTS

OK, the modules works now.

Tips

• __name__ in a module have different values with different referenced type
  • when imported, the value is the module name, as ‘os_info’
  • when excuted by python directly, the value is ‘main’
  • That’s why we have “if __name__ == '__main__'” code in modules

Source code refers to modulized_os_information.