How do modules and packages work in Python?

How do modules and packages work in Python?

As a powerful programming language, Python has a rich standard library and also supports custom modules and packages, which makes program organization and reuse simpler and more efficient. This article will introduce the basic concepts of modules and packages in Python and illustrate how they work through specific code examples.

1. The concept and use of modules

In Python, a module is a file containing functions, variables and classes. Each Python file can be regarded as an independent module and introduced into other programs for use through the import statement. The following is a simple module example, saved as an example_module.py file:

# example_module.py
PI = 3.14159

def circle_area(radius):
    return PI * radius * radius

def square_area(side_length):
    return side_length ** 2

In another program, you can use the import statement to import this module and call the functions in it:

import example_module

print(example_module.circle_area(2))
print(example_module.square_area(4))

Run The output results of the above code are 12.56636 and 16 respectively.

2. The Concept and Use of Packages

Package is a way to organize multiple modules. In Python, a package is a folder containing an __init__.py file. The __init__.py file can be an empty file, but its existence indicates that the folder is a package. The following is a simple package example, containing two modules circle.py and square.py, and an empty __init__.py file:

my_package/
    __init__.py
    circle.py
    square.py

The contents of the circle.py file are as follows:

# circle.py
PI = 3.14159

def area(radius):
    return PI * radius * radius

## The content of the #square.py file is as follows:

# square.py

def area(side_length):
    return side_length ** 2

In another program, you can use the import statement to import the package and call the modules and functions in it:

import my_package.circle
import my_package.square

print(my_package.circle.area(2))
print(my_package.square.area(4))

Run the above code and the output results are respectively is 12.56636 and 16.

3. How to import modules and packages

In addition to the above import statements, Python also provides several other import methods to meet different needs.

Import the specified function or variable from a module or package

1. from example_module import circle_area
   
   print(circle_area(2))

Specify an alias for the imported module or function

2. import example_module as em
   
   print(em.circle_area(2))

Import all modules in the package

3. from my_package import *
   
   print(circle.area(2))
   print(square.area(4))

4. Search paths for modules and packages

When Python imports a module, it will follow a certain search path to find the module. The search path includes the current directory, installed third-party libraries and Python standard libraries, etc. You can use the path attribute of the sys module to view the current search path:

import sys

print(sys.path)

Running the above code will output a list containing multiple paths.

5. Summary

This article introduces the basic concepts of modules and packages in Python, and demonstrates their usage through specific code examples. Modules and packages greatly improve the organization and reusability of programs, making programming simpler and more efficient. At the same time, mastering the import methods and search paths of modules and packages is also an important basis for writing Python programs.

I hope that through the introduction of this article, readers can better understand and apply how modules and packages in Python work. Learning more about the use of modules and packages will make Python programming more flexible and powerful.

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