Modules

A module is simply a file containing Python code that can define functions, classes, and variables. It is usually a collection of related functions and variables that you can use in your programs. These help you organize your programs and reuse code instead of writing it from scratch every time.

You can create your own modules, or use modules that come with Python. For example, Python has a math module that gives you access to mathematical functions and constants, like pi (π).

Here is a simple example of a module being used:

import math
print(math.pi)  # Prints the value of pi

Using a Module

To use a module, you first need to import it. You can do this using the import statement. For example, to import the math module, you would write:

# import <module_name>
import math

However, you can also import specific functions or variables from a module using the from keyword. For example, if you only want to use the sqrt function from the math module, you can do it like this:

# from <module_name> import <function_name>
from math import sqrt
print(sqrt(16))  # Prints 4.0

And, if you want to import all functions and variables from a module, you can use the * wildcard:

# from <module_name> import *
from math import * # this has imported everything from the math module
print(sqrt(16))  # Prints 4.0
print(pi)  # Prints the value of pi

Note: Using * is not recommended because it can lead to confusion if there are functions or variables with the same name in different modules. This is also known as "namespace pollution".

You can also provide an alias (or another name) for a module using the as keyword. This is useful if the module name is long or if you want to avoid name conflicts. For example:

# import <module_name> as <alias>
import math as math_module 
print(math_module.pi)  # Prints the value of pi

Note: The alias can be any name you choose, but it's common to use a shortened version of the module name (numpy is often imported as np, for example). Or a descriptive name that indicates what the module does.

Creating Your Own Modules

Creating a module in python is as simple as creating a new python file and adding your functions and variables to it. The online code editor will not allow you to do this; however, you can follow along locally on your computer (see "introduction"). Start by creating a file my_module.py and add the following code to it (otherwise, just read along):

def greet(name):
    print(f"Hello, {name}!")

def add(a, b):
    return a + b

After creating this file, you can use it in another python file by importing it. For example:

# Please note that the file name is the module name
# and it should be in the same directory as the file you are importing it into
# or in the Python path.
import my_module

my_module.greet("Alice")  # Prints "Hello, Alice!"
print(my_module.add(2, 3))  # Prints 5

Then, name this file main.py and run it with the command:

python main.py

and you should see the following output:

Hello, Alice!
5

Thats (mostly) it! You can now create your own modules and use them in your program. We will cover more advanced topics like packages (open source libraries online) and how to create your own packages.

DocStrings

Docstrings are strings used to document modules, functions, classes, and methods in Python. Inside this, you can provide information about the code's purpose, parameters, returns, etc. For example:

def greet(name):
    """Greets a person by name.

    Args:
        name (str): The name of the person to greet.

    Returns:
        None
    """
    print(f"Hello, {name}!")

Docstrings improve code readability and are often used with tools like help() or documentation generators (e.g., Sphinx). They are optional but highly recommended for maintainability.