Functions are reusable blocks of code that perform specific tasks. Here’s how to create them in Python.

Basic Function Definition

Use the def keyword to define a function:

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

print(greet("Alice"))  # "Hello, Alice!"

Functions with Multiple Parameters

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

result = add(3, 5)
print(result)  # 8

Default Parameters

Provide default values for optional parameters:

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

print(greet("Alice"))              # "Hello, Alice!"
print(greet("Bob", "Hi"))          # "Hi, Bob!"

Keyword Arguments

Call functions with named arguments:

def describe_person(name, age, city):
    return f"{name} is {age} years old and lives in {city}"

# Using keyword arguments (order doesn't matter)
print(describe_person(age=25, city="Paris", name="Alice"))

*args and **kwargs

Accept variable numbers of arguments:

# *args for variable positional arguments
def sum_all(*numbers):
    return sum(numbers)

print(sum_all(1, 2, 3, 4))  # 10

# **kwargs for variable keyword arguments
def print_info(**kwargs):
    for key, value in kwargs.items():
        print(f"{key}: {value}")

print_info(name="Alice", age=25, city="Paris")

Lambda Functions

Create small anonymous functions:

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

# Lambda equivalent
square = lambda x: x ** 2

print(square(5))  # 25

Summary

Use def to define functions
Use default parameters for optional arguments
Use *args and **kwargs for flexible argument handling
Use lambda for simple, one-line functions

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