Python Concept - Script, Module, library, function and classes

Important concept of Python 2021

Understanding Script, module, package,  library

·         Script: python file that run directly to perform certain task.

 

·         Module: Python file that is imported in script or another program. It defines member like classes, functions and variable intended to be used in other files that import it.

 

·         Python.org definition: An object that serves as an organizational unit of Python code. Modules have a namespace containing arbitrary Python objects. Modules are loaded into Python by the process of importing.

 

·         Package:  collection of related modules that work together to provide certain functionality. This are folder containing modules. It has special file with name __init__.py

 

·         Python.org definition : A Python module which can contain submodules or recursively, subpackages. Technically, a package is a Python module with an __path__ attribute.

 

·         To create Python package ourself, we have to create directory and a file named __init__.py inside it. This file cab be empty.

 

·         Note: Directories without an __init__.py file are still treated as packages by Python. However, these won’t be regular packages, but something called namespace packages.

 

·         In general, submodules and subpackages aren’t imported when you import a package. However, you can use __init__.py to include any or all submodules and subpackages if you want.

 

·         Library: a bundle of code / collection of packages. E.g. Matplotlib (plotting libaray)

o   Standard library (available by default)

o   3rd-Party Modules

 

 

Understanding import methods / option:

It is python keyword to make code in one module available in another. They help to structure code.

 

Method 1: Basic import:

Here pi is variable in math module.

Math acts as namespace (In computing, a namespace is a set of signs (names) that are used to identify and refer to objects of various kinds. )

To see content of math module you can use dir(math)

 

Method 2: import specific part (objects) from module

 

 

Method 3: import with rename

 

Importing module gives access to its objects using syntax: module.object

 

 

 

Method 4: Relative import.

From . import <sum-package-name>

The dot refers to the current package, and the statement is an example of a relative import. You can read it as “From the current package, import the subpackage <sum-package-name>”

 

 

 

Method 5 absolute import:

From math import pi

 

The PEP 8 style guide recommends using absolute imports in general. However, relative imports are an alternative for organizing package hierarchies. For more information, see Absolute vs Relative Imports in Python.

Don’t use from <module> import *

 

Python import path:

You can inspect Python’s import path by using sys.path.

 

List will contain three different kinds of locations:

·         The directory of the current script / current directory

·         The contents of the PYTHONPATH environment variable.

·         Other, installation-dependent direcotires.

 

Note 1: clearing import catch

Modules are cached, if we update module then we need to re-import it in old session and delete old cache.

That can be done using

Reload(<module-name>)

 

For Python3 (its not available by default)

Import  importlib

Importlib.reload(<module-name>)

 

Note 2:  __main__

Sometimes we want code to be executed when module is run directly , but not when it is imported by another module.

If  __name__ == ‘__main__’   allows us to check whether the module is being run directly.

 

 

 

Understanding function, class

Function is set of code that can be called repeatedly

 

 

What is Class ?

Object oriented programming (OOP):

OOP terms:

·         Class

·         object

Object has two parameters:

1.    Attributes (data / properties e.g. age, name etc)

2.    Behaviors (action walking, talking etc)

 

E.G. phone is object, but its design is class and object is instance.

Object is instance of class.

Function is OOP is called method.

 

 

·         Class can be considered as template for creating object with related data (attributes) and function (action) that do interesting thing with that data.

 

·         Class help to create customized data type

 

·         Function inside the class is called method.

 

·          

 

 

# Creating class Example 1

Class User:

     Pass

 

Note: pass is a sort of place holder.

 

Creating object

# User1

 

User1=User()

 

# Creating class Example 2

 

 

 

 

 

 

 

 

To use instance variable inside class function we can use self.<instance-variable-name>

 

 

Creating class with variable Example #3

Class Router:
    ‘’’Router Class’’’
    def __init__(self,model,swversion,ip_add):
        ‘’’initialize values’’’
        self.mode=model
        self.swversion=swversion
        self.ip_add=ip_add

 

 rtr1=Router(“ios”,”15.6.7”,”10.10.10.1”)

 

Function __init__  is called dunder or magic methods.

To store attributes we map the name self and the value you pass to it become variables inside the object, which is then store those value as attributes.

 

>>> rtr1.model

“ios”

 

We can define additional variable later.

>>> rtr1.desc =”virtual router”

>>> rtr1.desc

“virtual router”

 

Inheritance in Python classes allow a child class to take on attributes and methods of another class.

Class Switch(Router):

Here class Switch inherits the attribute of parent class Router.

 

 

 

 

 

Killing window application via python

Import os

os.system("taskkill /f /im notepad.exe")
os.system("taskkill /f /im winword.exe")
os.system("taskkill /f /im excel.exe")
os.system("taskkill /f /im powerpnt.exe")
os.system("taskkill /f /im outlook.exe")
os.system("taskkill /f /im chrome.exe")
os.system("taskkill /f /im calc.exe")
os.system("taskkill /f /im iexplore.exe")
os.system("taskkill /f /im powershell.exe")
os.system("taskkill /f /im wordpad.exe")