Defining Functions in Python Using the def Keyword

Introduction

Functions are reusable blocks of code that perform a specific task. In Python, functions are defined using the def keyword. They make programs more modular, readable, and easier to maintain. This article explains how to define and use functions in Python with examples.

Syntax of a Function

The basic syntax of a function in Python is as follows:

    def function_name(parameters):
        # Code block
        return result

Explanation:

  • def: Keyword to define a function.
  • function_name: Name of the function.
  • parameters: Optional arguments the function takes (can be empty).
  • return: Optional statement to return a result from the function.

Example: A Simple Function

The following example defines and calls a function that prints a greeting:

    # Example of a simple function
    def greet():
        print("Hello, World!")
        
    # Calling the function
    greet()

Output:

    Hello, World!

Example: Function with Parameters

Functions can take parameters to make them more flexible. The following example demonstrates a function that takes a name as input:

    # Function with parameters
    def greet_person(name):
        print(f"Hello, {name}!")
        
    # Calling the function with an argument
    greet_person("Alice")

Output:

    Hello, Alice!

Example: Function with Return Value

A function can return a value using the return statement. The following example defines a function that calculates the square of a number:

    # Function with return value
    def square(number):
        return number * number
        
    # Calling the function and storing the result
    result = square(4)
    print("The square is:", result)

Output:

    The square is: 16

Example: Function with Default Parameters

Functions can have default parameter values. These are used if no argument is provided during the function call.

    # Function with default parameter
    def greet_with_time(name, time_of_day="morning"):
        print(f"Good {time_of_day}, {name}!")
        
    # Calling the function with and without the second argument
    greet_with_time("Alice", "afternoon")
    greet_with_time("Bob")

Output:

    Good afternoon, Alice!
    Good morning, Bob!

Example: Function with Multiple Parameters

The following example defines a function that adds two numbers:

    # Function with multiple parameters
    def add_numbers(a, b):
        return a + b
        
    # Calling the function with two arguments
    sum_result = add_numbers(3, 7)
    print("The sum is:", sum_result)

Output:

    The sum is: 10

Conclusion

Functions are a core feature of Python that make code more organized and reusable. By understanding how to define functions and use parameters and return values, you can write efficient and modular Python programs. Experiment with these examples to deepen your understanding of functions.




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