Functions

Functions

Functions are first-class objects in Python — they can be passed as arguments, returned from other functions, and stored in variables.

def and return

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

result = add(3, 4)  # 7

Default Arguments

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

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

*args and **kwargs

def total(*args):        # collects positional args into tuple
    return sum(args)

def info(**kwargs):      # collects keyword args into dict
    for k, v in kwargs.items():
        print(f"{k}: {v}")

total(1, 2, 3)           # 6
info(name="Alice", age=30)

Functions as Arguments

def apply(f, x):
    return f(x)

apply(abs, -5)           # 5
apply(str.upper, "hi")   # "HI"

Lambda

double = lambda x: x * 2
double(4)  # 8

Your Task

Implement apply_twice(f, x) that applies function f to x twice: f(f(x)).