Create and Access a Python Package

Packages are a way of structuring many packages and modules which helps in a well-organized hierarchy of data set, making the directories and modules easy to access. Just like there are different drives and folders in an OS to help us store files, similarly packages help us in storing other sub-packages and modules, so that it can be used by the user when necessary.

Creating and Exploring Packages

To tell Python that a particular directory is a package, we create a file named __init__.py inside it and then it is considered as a package and we may create other modules and sub-packages within it. This __init__.py file can be left blank or can be coded with the initialization code for the package. To create a package in Python, we need to follow these three simple steps:

1. First, we create a directory and give it a package name, preferably related to its operation.
2. Then we put the classes and the required functions in it.
3. Finally we create an __init__.py file inside the directory, to let Python know that the directory is a package.

Example of Creating Package

Let's look at this example and see how a package is created. Let's create a package named Cars and build three modules in it namely, Bmw, Audi and Nissan.

1. First we create a directory and name it Cars.
2. Then we need to create modules. To do this we need to create a file with the name Bmw.py and create its content by putting this code into it. Python

   # Python code to illustrate the Modules
   class Bmw:
       # First we create a constructor for this class
       # and add members to it, here models
       def __init__(self):
           self.models = ['i8', 'x1', 'x5', 'x6']
    
       # A normal print function
       def outModels(self):
           print('These are the available models for BMW')
           for model in self.models:
               print('\t%s ' % model)
   

   Then we create another file with the name Audi.py and add the similar type of code to it with different members. Python

   # Python code to illustrate the Module
   class Audi:
       # First we create a constructor for this class
       # and add members to it, here models
       def __init__(self):
           self.models = ['q7', 'a6', 'a8', 'a3']
   
       # A normal print function
       def outModels(self):
           print('These are the available models for Audi')
           for model in self.models:
               print('\t%s ' % model)
   

   Then we create another file with the name Nissan.py and add the similar type of code to it with different members. Python

   # Python code to illustrate the Module
   class Nissan:
       # First we create a constructor for this class
       # and add members to it, here models
       def __init__(self):
           self.models = ['altima', '370z', 'cube', 'rogue']
   
       # A normal print function
       def outModels(self):
           print('These are the available models for Nissan')
           for model in self.models:
               print('\t%s ' % model)
   

3. Finally we create the __init__.py file. This file will be placed inside Cars directory and can be left blank or we can put this initialisation code into it. Python

   from Bmw import Bmw
   from Audi import Audi
   from Nissan import Nissan
   

Now, let's use the package that we created. To do this make a sample.py file in the same directory where Cars package is located and add the following code to it: Python

# Import classes from your brand new package
from Cars import Bmw
from Cars import Audi
from Cars import Nissan
 
# Create an object of Bmw class & call its method
ModBMW = Bmw()
ModBMW.outModels()
 
# Create an object of Audi class & call its method
ModAudi = Audi()
ModAudi.outModels()

# Create an object of Nissan class & call its method
ModNissan = Nissan()
ModNissan.outModels()

Various ways of Accessing the Packages

Let's look at this example and try to relate packages with it and how can we access it.
1. import in Packages Suppose the cars and the brand directories are packages. For them to be a package they all must contain __init__.py file in them, either blank or with some initialization code. Let’s assume that all the models of the cars to be modules. Use of packages helps importing any modules, individually or whole. Suppose we want to get Bmw i8. The syntax for that would be:

   'import' Cars.Bmw.x5 

   While importing a package or sub packages or modules, Python searches the whole tree of directories looking for the particular package and proceeds systematically as programmed by the dot operator. If any module contains a function and we want to import that. For e.g., a8 has a function get_buy(1) and we want to import that, the syntax would be:

   import Cars.Audi.a8
   Cars.Audi.a8.get_buy(1)
   

   While using just the import syntax, one must keep in mind that the last attribute must be a subpackage or a module, it should not be any function or class name.
2. 'from...import' in Packages Now, whenever we require using such function we would need to write the whole long line after importing the parent package. To get through this in a simpler way we use 'from' keyword. For this we first need to bring in the module using 'from' and 'import':

   from Cars.Audi import a8

   Now we can call the function anywhere using

   a8.get_buy(1)

   There's also another way which is less lengthy. We can directly import the function and use it wherever necessary. First import it using:

   from Cars.Audi.a8 import get_buy

   Now call the function from anywhere:

   get_buy(1)

3. 'from...import *' in Packages While using the from...import syntax, we can import anything from submodules to class or function or variable, defined in the same module. If the mentioned attribute in the import part is not defined in the package then the compiler throws an ImportError exception. Importing sub-modules might cause unwanted side-effects that happens while importing sub-modules explicitly. Thus we can import various modules at a single time using * syntax. The syntax is:

   from Cars.Chevrolet import *

   This will import everything i.e., modules, sub-modules, function, classes, from the sub-package.


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Chinmoy Lenka

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