Package

We organize a large number of files in different folders and subfolders based on some criteria, so that we can find and manage them easily. In the same way, a package in Python takes the concept of the modular approach to next logical level. As you know, a module can contain multiple objects, such as classes, functions, etc. A package can contain one or more relevant modules. Physically, a package is actually a folder containing one or more module files.

Besides, package can avoid module name conflicts as well.

Package

Let's create a package named mypackage in MyApp folder, liking the following structure:

MyApp
  └─ mypackage
     ├─ __init__.py
     ├─ greet.py
     └─ functions.py

greet.py

def SayHello(name):
    print("Hello ", name)

functions.py

def sum(x,y):
    return x+y

def average(x,y):
    return (x+y)/2

def power(x,y):
    return x**y

That's it. We have created our package called mypackage. The following is a folder structure:

Figure: Package Folder Structure

Importing a Module from a Package

Now, to test our package, navigate the command prompt to the MyApp folder and invoke the Python prompt from there.

(base) ➜  MyApp python

Import the functions module from the mypackage package and call its power() function.

>>> from mypackage import functions
>>> functions.power(3,2)
9

It is also possible to import specific functions from a module in the package.

>>> from mypackage.functions import sum

>>> sum(10,20)
30

>>> average(10,12)
Traceback (most recent call last):
File "<pyshell#13>", line 1, in <module>
NameError: name 'average' is not defined

__init__.py

The package folder contains a special file called __init__.py, which stores the package's content. It serves two purposes:

• The Python interpreter recognizes a folder as the package if it contains __init__.py file.
• __init__.py exposes specified resources from its modules to be imported.

An empty__init__.py file makes all functions from the above modules available when this package is imported.

tip

__init__.py is essential for the folder to be recognized by Python as a package. Otherwise, Python treats this folder as a normal folder instead of a package. __init__.py can be an empty file or have Python code, because the __init.py__ itself is a module, and its module name is mypackage.

The __init__.py file is normally kept empty. However, it can also be used to choose specific functions from modules in the package folder and make them available for import. Modify __init__.py as below:

__init__.py

from .functions import average, power
from .greet import SayHello

The specified functions can now be imported in the interpreter session or another executable script.

Create test.py in the MyApp folder to test mypackage.

MyApp/test.py

from mypackage import power, average, SayHello

SayHello()
x = power(3,2)
print("power(3,2) : ", x)

tip

The functions power() and SayHello() are imported from the package and not from their respective modules, as done earlier.

The output of the above script is:

(base) ➜  MyApp python test.py
Hello world
power(3,2) : 9

Install a Package Globally

Once a package is created, it can be installed for system-wide use by running the setup script. The script calls setup() function from the setuptools module.

Let's install mypackage for system-wide use by running a setup script.

Save the following code as setup.py in the parent folder MyApp.

The script calls the setup() function from the setuptools module. The setup() function takes various arguments such as name, version, author, list of dependencies, etc. The zip_safe argument defines whether the package is installed in compressed mode or regular mode.

MyApp/setup.py

from setuptools import setup

setup(name='mypackage',
version='0.1',
description='Testing installation of Package',
url='#',
author='auth',
author_email='author@email.com',
license='MIT',
packages=['mypackage'],
zip_safe=False)

Now execute the following command to install mypackage using the pip utility. Ensure that the command prompt is in the parent folder, in this case ~\MyApp.

(base) ➜  MyApp pip install mypackage
Processing ~\MyApp
Installing collected packages: mypack
Running setup.py install for mypack ... done
Successfully installed mypackage-0.1

Now mypackage is available for system-wide use and can be imported in any script or interpreter.

(base) ➜  MyApp python
>>> import mypackage
>>>mypackage.average(10,20)
15.0
>>>mypackage.power(10,2)
100

You may also want to publish the package for public use. PyPI (stands for Python Package Index) is a repository of Python packages. Visit https://packaging.python.org/distributing to know more about the procedure of uploading a package to PyPI.

Reference

1. Python Packages by tutorials teacher