Modules

Understanding Python Modules

A module in Python is essentially a code library—a file that encapsulates a collection of functions, variables, or classes that you can include in your application. Modules are a powerful way to organize and reuse code across different projects.

Creating Your Own Module

To create a module, simply write the functions or variables you want to include in a file with the .py extension.

Example: Save the following code in a file named mymodule.py.

def greeting(book_name):
    print("Hello, " + book_name)

In this example, the greeting function is defined to greet a specific book by its name.

Using a Custom Module

Once you’ve created your module, you can import it into any Python script using the import statement.

Example: Import the module mymodule and call its greeting function.

import mymodule

mymodule.greeting("The Great Gatsby")
# Expected output: Hello, The Great Gatsby

When you call a function from a module, the syntax is straightforward: module_name.function_name. The result is visible in the comment above.

Including Variables in a Module

In addition to functions, a module can also contain variables of any type, such as arrays, dictionaries, or objects.

Example: Save this code in mymodule.py.

book1 = {
    "title": "1984",
    "pages": 328,
    "author": "George Orwell"
}

Now, you can import the module and access the variables it contains.

import mymodule

a = mymodule.book1["pages"]
print(a)
# Expected output: 328

Naming and Renaming Modules

You can name your module file whatever you like, as long as it has the .py extension. Additionally, when importing a module, you can create an alias using the as keyword.

Example: Create an alias for mymodule and access its variables.

import mymodule as mx

a = mx.book1["pages"]
print(a)
# Expected output: 328

Exploring Built-in Modules

Python comes with several built-in modules that you can import and use without needing to create them yourself.

Example: Import the platform module and use it to determine the system type.

import platform

x = platform.system()
print(x)
# Expected output could be: Linux, Windows, or Darwin (for macOS)

Using the dir() Function

The dir() function is a built-in Python function that lists all the function names (or variable names) defined in a module.

Example: List all the attributes of the platform module.

import platform

x = dir(platform)
print(x)
# Expected output: A list of all attributes in the platform module, such as ['architecture', 'machine', 'node', 'platform', 'processor', 'python_version', 'system', etc.]

The dir() function can be used on any module, including those you create yourself.

Importing Specific Elements from a Module

Sometimes, you might want to import only certain parts of a module. This can be done using the from keyword.

Example: The mymodule module contains a function and a dictionary:

def greeting(book_name):
    print("Hello, " + book_name)

book1 = {
    "title": "1984",
    "pages": 328,
    "author": "George Orwell"
}

You can choose to import only the dictionary book1 from the module.

from mymodule import book1

print(book1["pages"])
# Expected output: 328

Note that when you use the from keyword, you should refer to the imported elements directly, without using the module name.