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Github project link – https://github.com/kuldeep101990/Python_step7

Modules and packages are fundamental for structuring and organizing code in Python. If you’re familiar with Java packages, you’ll find many similarities, with Python’s approach being more dynamic and flexible.

Importing Modules (import vs. Java import)

In Java, we use import to include predefined classes from packages, such as java.util.ArrayList. Similarly, Python uses import to include external or user-defined modules.

Java Example:

import java.util.ArrayList;
public class Main {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
        list.add("Hello");
        System.out.println(list);
    }
}

Python Equivalent:

import math
# Using the imported module
print(math.sqrt(16))

• In Python, you can also import specific functions or classes from a module:

from math import sqrt
print(sqrt(16))

Standard Python Libraries

Python comes with an extensive standard library, equivalent to Java’s standard library. Here are some commonly used modules:

1. os: Interact with the operating system.
2. sys: Access system-specific parameters and functions.
3. math: Perform mathematical operations.
4. datetime: Handle dates and times.

Example Usage:

import os
print("Current working directory:", os.getcwd())
import sys
print("Python version:", sys.version)
import math
print("Pi value:", math.pi)
from datetime import datetime
print("Current date and time:", datetime.now())

Creating and Using Packages

Packages in Python are directories containing a special __init__.py file (this file can be empty). They help organize modules into namespaces.

Creating a Package in Python:

1. Create a folder named mypackage.
2. Inside it, create:
   • __init__.py: Marks the directory as a package.
   • module1.py: Contains Python functions or classes.

Folder Structure:

mypackage/
    __init__.py
    module1.py

Example Content of module1.py:

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

Using the Package:

from mypackage import module1
print(module1.greet("Alice"))

The __name__ == "__main__" Construct

In Java, the main method is the entry point for execution. In Python, we use the __name__ == "__main__" construct to determine if a script is being run directly or imported as a module.

Java Example:

public class Main {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

Python Equivalent:

def main():
    print("Hello, World!")
if __name__ == "__main__":
    main()

When a Python file is run directly, its __name__ is set to "__main__". If the file is imported, __name__ is set to the module’s name.

Complete Python Program

Here’s a program that demonstrates modules, packages, and the __name__ == "__main__" construct:

Folder Structure:

mypackage/
    __init__.py
    calculator.py
main.py

Content of calculator.py:

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

Content of main.py:

from mypackage.calculator import add, subtract
def main():
    print("Addition:", add(5, 3))
    print("Subtraction:", subtract(5, 3))
if __name__ == "__main__":
    main()

How to Run:

1. Save the files as per the folder structure.
2. Run the main.py file: python main.py

Sample Output:

Addition: 8
Subtraction: 2

By understanding and leveraging modules and packages, you can create modular, maintainable, and reusable Python code. Try these examples to deepen your knowledge!