Python Module System Guide

Python's module system helps organize code into reusable units. Modules are files containing Python definitions and statements. They make code easier to manage.

What Are Python Modules?

A module is a file with a .py extension. It can contain functions, classes, and variables. Modules help break large programs into smaller files.

Here's a simple module example:

# mymodule.py
def greet(name):
    return f"Hello, {name}!"

version = "1.0"

How Python Imports Modules

Use the import statement to load modules. Python searches for modules in specific locations. The search path includes the current directory and installed packages.

Basic import example:

import mymodule

print(mymodule.greet("Alice"))  # Output: Hello, Alice!
print(mymodule.version)         # Output: 1.0

For more details, see our Python Import Statements Guide.

Module Namespaces

Each module has its own namespace. This prevents naming conflicts. Attributes are accessed using dot notation.

Namespace example:

import math

print(math.pi)  # Output: 3.141592653589793

Different Import Methods

Python offers several ways to import modules:

• import module - Basic import
• from module import name - Import specific names
• import module as alias - Import with alias

Example of alternative imports:

from mymodule import greet

print(greet("Bob"))  # No need for module prefix

Learn best practices in our Python Import vs Import: Best Practices guide.

Python's Import System

Python's import system is powerful. It uses finders and loaders to locate and load modules. The system is extensible.

Key components:

• sys.path - Module search path
• importlib - Implementation of import
• Module cache - Stores loaded modules

For advanced topics, see the Python Import System Guide.

Package Organization

Packages are collections of modules. They use __init__.py files. Packages create hierarchical namespaces.

Example package structure:

mypackage/
    __init__.py
    module1.py
    module2.py
    subpackage/
        __init__.py
        module3.py

Special Module Attributes

Modules have special attributes:

• __name__ - Module name
• __file__ - Path to module file
• __package__ - Package name

Example usage:

import mymodule

print(mymodule.__name__)  # Output: mymodule
print(mymodule.__file__)  # Output: path/to/mymodule.py

Module Execution

Modules can be run as scripts. Use if __name__ == "__main__": to control execution. This makes modules more flexible.

Example:

# mymodule.py
def greet(name):
    return f"Hello, {name}!"

if __name__ == "__main__":
    print(greet("World"))

Built-in Modules

Python comes with many built-in modules. These provide useful functionality. Examples include math, os, and sys.

Built-in module example:

import os

print(os.getcwd())  # Output: current working directory

Conclusion

Python's module system is essential for code organization. It helps create maintainable programs. Understanding modules makes you a better Python programmer.

Use modules to structure your code logically. Follow best practices for imports. Leverage packages for complex projects.