Functions

In programming, a function is a reusable block of code that executes a certain functionality when it is called.They play a vital role in modularizing code, improving readability, and promoting code reusability. This tutorial provides an overview of Python functions, including their creation, parameters, return values, and usage.

Creating a Function

You can create a function in Python using the def keyword, followed by the function name and a pair of parentheses (). The function body is indented below the function definition.

      def greet():
          print("Hello, World!")
      

Function Parameters

Functions can take input values known as parameters or arguments, allowing you to customize their behavior based on the input.

      def greet_user(username):
          print(f"Hello, {username}!")
      

Function Invocation

To execute a function, you need to call it by its name, followed by a pair of parentheses ().

      # Calling the function without parameters
      greet()

      # Calling the function with a parameter
      greet_user("Alice")
      

Return Values

Functions can return values using the return statement. The returned value can be assigned to a variable or used directly.

      def add_numbers(a, b):
          # Function to add two numbers
          return a + b

      # Calling the function and storing the result in a variable
      result = add_numbers(10, 5)
      print(result)  # Output: 15

      # Using the function directly in an expression
      sum_result = add_numbers(3, 7) + add_numbers(2, 8)
      print(sum_result)  # Output: 20
      

Default Parameters

You can provide default values for parameters in a function. If a value is not passed for that parameter during the function call, the default value is used.

      def greet_user(username="Guest"):
          print(f"Hello, {username}!")

      # Calling the function without passing a value
      greet_user()  # Output: Hello, Guest!

      # Calling the function with a custom value
      greet_user("Alice")  # Output: Hello, Alice!
      

Variable-Length Arguments

Python allows you to define functions that can accept a variable number of arguments using *args (for non-keyword arguments) and **kwargs (for keyword arguments).

      def add_all_numbers(*args):
          # Function to add all numbers passed as arguments
          total = 0
          for num in args:
              total += num
          return total

      # Calling the function with different numbers of arguments
      result1 = add_all_numbers(1, 2, 3, 4)
      result2 = add_all_numbers(10, 20, 30, 40, 50)
      print(result1)  # Output: 10
      print(result2)  # Output: 150
      

Lambda Functions

Lambda functions are small, anonymous functions defined using the lambda keyword.

      # Regular function to square a number
      def square(x):
          return x ** 2

      # Equivalent lambda function
      square_lambda = lambda x: x ** 2

      # Using the lambda function
      print(square_lambda(5))  # Output: 25