Python Packages

What Is a Package in Python?

A package is a folder that contains Python modules. It can also contain subpackages. It helps us group related code.

Think of a package like a folder on your computer. You put related files inside. Instead of having one big module, we split it into smaller modules and put them in a package.

Why Do We Need Packages in Python?

As our programs grow, we may have many modules. Putting them all in one folder becomes messy. Packages let us organize them into subfolders.

Packages also make it easier to share code. We can create a package and install it on other computers.

How to Create a Package in Python

A package is just a folder with a special file called __init__.py inside. That file can be empty. It tells Python that the folder is a package.

Let us create a package called mypackage.

mypackage/
    __init__.py
    math_utils.py
    string_utils.py

The __init__.py file is empty. The math_utils.py and string_utils.py are modules.

How to Use a Package in Python

Now we can import modules from the package.

from mypackage import math_utils, string_utils

print(math_utils.add(5, 3))
print(string_utils.reverse_string("hello"))

8
olleh

We can also import specific functions.

from mypackage.math_utils import add

print(add(5, 3))

8

Adding Code to init.py

The __init__.py file can be empty. But we can also put code in it. That code runs when the package is imported.

print("mypackage is being imported")

Now when we import the package, we see the message.

import mypackage

mypackage is being imported

That is useful for setting up the package.

Subpackages in Python

A package can contain subpackages. A subpackage is a folder inside a package with its own __init__.py.

mypackage/
    __init__.py
    math_utils.py
    string_utils.py
    subpackage/
        __init__.py
        advanced_math.py

We can import from the subpackage.

from mypackage.subpackage import advanced_math

advanced_math.do_something()

That is how we organize large projects.

A Real-Life Example – A Utility Package

Let us create a package called utils with two modules: file_utils.py and string_utils.py.

utils/
    __init__.py
    file_utils.py
    string_utils.py

file_utils.py:

def read_file(filename):
    with open(filename, "r") as file:
        return file.read()

def write_file(filename, content):
    with open(filename, "w") as file:
        file.write(content)

string_utils.py:

def reverse(s):
    return s[::-1]

def capitalize_words(s):
    return s.title()

Now we can use this package in our main program.

from utils import file_utils, string_utils

string_utils.write_file("test.txt", "hello world")
print(file_utils.read_file("test.txt"))
print(string_utils.reverse("Python"))
print(string_utils.capitalize_words("hello world"))

hello world
nohtyP
Hello World

That is a clean and organized package.

Common Mistakes with Packages in Python

from mypackage.math_utils import add