What is a Python Module?

A module is simply a file that contains Python code, which may include functions, classes, and variables. Files with a .py extension are recognized as Python modules. You can create a module using any text editor. For instance, consider a file named sum_n.py that includes the following code:

To use the sum_n module in the Python interpreter, you would write:

import sum_n

To call the function sum_of_numbers, you would proceed as follows:

sum_n.sum_of_numbers([10, 13, 23, 24])

Alternatively, you can directly import the function:

from sum_n import sum_of_numbers

If you have multiple statements in sum_n.py, you can import everything from the module using:

from sum_n import *

This grants access to both the sum_of_numbers function and any classes defined within the module.

What is a Python Package?

A package is essentially a directory that contains multiple modules. In simpler terms, a package can be seen as a folder that may include subfolders, each housing their own modules. For example, the following structure represents a root package:

app/

__init__.py

models.py

views.py

util/

Python also provides built-in modules, such as the datetime module, which enables date and time manipulation. To utilize the datetime class, you would start by importing it:

from datetime import datetime

You can retrieve the current time with:

current_time = datetime.now()

print(current_time)

This will yield an output similar to:

2022-02-17 11:57:45.910122

Another built-in module is the math module, which allows for mathematical operations. For example, to access the value of pi, you would do:

import math

pi_constant = math.pi

print(pi_constant)

The output is:

3.141592653589793

Some modules require installation before use; for instance, to use matplotlib, you must first install it via pip:

pip install matplotlib

If you skip this step, you will encounter an import error:

ModuleNotFoundError: No module named 'matplotlib'

Importing Modules with Aliases

When module names are lengthy, you can create an alias using the as keyword. The syntax for this is:

import module_name as module_alias

For instance, to import the pyplot function as plt, you would write:

import matplotlib.pyplot as plt

plt.plot([10, 20, 30, 40])

plt.ylabel('Minimum values')

plt.show()

Organizing Imports

The Python PEP 8 style guide outlines several conventions for imports. The recommended order is:

1. Standard library imports
2. Third-party imports
3. Local application imports

A blank line should separate each import group. Additionally, imports should be listed on separate lines, for example:

import os

import sys

Absolute Imports

Absolute imports specify the complete path to the function being imported, starting from the root directory. Consider creating a directory called my_project with the following structure:

my_project/

collection1/

__init__.py

file_a.py

collection2/

__init__.py

file_b.py

In file_a.py, you might define:

def english_greeting():

print("Long time, no see")

And in file_b.py, you could include:

def german_greeting():

print("Lange nicht gesehen")

To import these functions using the Python interpreter, you would write:

from collection1.file_a import english_greeting

from collection2.file_b import german_greeting

Relative Imports

Relative imports are designated based on the file's location from which they are being imported, utilizing dot notation. In a Django project, for example, the directory structure might look like this:

member_app/

Here’s how you would import the Member class in forms.py:

from .models import Member