Packages in Python

Unit 3 - 3.3  Packages in Python

1. What is a Package in Python?

A package in Python is a collection of related modules stored in a directory. It helps in organizing large codebases by grouping related functionality together.

A package must contain a special file named __init__.py (though optional in Python 3.3+, it's recommended to explicitly include it).

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Python packages are a way to organize and structure code by grouping related modules into directories. A package is essentially a folder that contains an __init__.py file and one or more Python files (modules). This organization helps manage and reuse code effectively, especially in larger projects. It also allows functionality to be easily shared and distributed across different applications. Packages act like toolboxes, storing and organizing tools (functions and classes) for efficient access and reuse.

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2. Structure of a Python Package

A package is simply a directory containing multiple Python modules.

Example Package Structure:

mypackage/

│── __init__.py

│── module1.py

│── module2.py

│── subpackage/

│   ├── __init__.py

│   ├── module3.py

• mypackage/ → Main package directory
• __init__.py → Makes the directory a package
• module1.py and module2.py → Contain Python functions/classes
• subpackage/ → A package within a package

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3. Creating a Python Package

Step 1: Create a Package Directory

Let's create a package named mypackage.

mkdir mypackage

Step 2: Add an __init__.py File

Create a file inside mypackage/ named __init__.py.

# __init__.py

print("mypackage is imported")

Step 3: Create Some Modules

Create two Python files inside mypackage/:

module1.py

def greet(name):

    return f"Hello, {name}!"

module2.py

def add(a, b):

    return a + b

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4. Importing a Package in Python

After creating the package, we can now use it in another Python script.

a) Importing the Whole Package

import mypackage.module1

import mypackage.module2

print(mypackage.module1.greet("Alice"))  # Output: Hello, Alice!

print(mypackage.module2.add(5, 3))  # Output: 8

b) Importing Specific Functions

from mypackage.module1 import greet

from mypackage.module2 import add

print(greet("Bob"))  # Output: Hello, Bob!

print(add(10, 2))  # Output: 12

c) Importing All Modules (Using __init__.py)

Modify __init__.py to automatically import modules:

from .module1 import greet

from .module2 import add

Now, you can directly import the package:

import mypackage

print(mypackage.greet("Charlie"))  # Output: Hello, Charlie!

print(mypackage.add(7, 3))  # Output: 10

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5. Subpackages in Python

A subpackage is a package inside another package.

Creating a Subpackage

mypackage/

│── __init__.py

│── module1.py

│── subpackage/

│   ├── __init__.py

│   ├── module3.py

subpackage/module3.py

def multiply(a, b):

    return a * b

Importing from a Subpackage

from mypackage.subpackage.module3 import multiply

 

print(multiply(4, 5))  # Output: 20

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6. Installing and Using External Packages

Python allows installing third-party packages using pip.

Installing a Package

pip install requests

Using an Installed Package

import requests

response = requests.get("https://www.google.com")

print(response.status_code)  # Output: 200

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7. Advantages of Using Packages

✅ Modularity – Organizes large codebases.
✅ Reusability – Functions can be reused across multiple projects.
✅ Avoids Name Conflicts – Helps prevent variable/function name clashes.
✅ Scalability – Makes it easy to expand and maintain projects.

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8. Summary

• A package is a directory containing multiple modules and an __init__.py file.
• Subpackages allow organizing related functionality even further.
• Importing can be done using import package.module, from package import module, or from package import *.
• Third-party packages can be installed using pip.