Higher-Order Functions

Definition

Functions that: 1. Take functions as arguments 2. Return functions

Take Functions

1. Apply Function

def apply_twice(func, value):
    return func(func(value))

def add_one(x):
    return x + 1

print(apply_twice(add_one, 5))  # 7

Return Functions

1. Function Factory

def make_multiplier(n):
    def multiply(x):
        return x * n
    return multiply

double = make_multiplier(2)
triple = make_multiplier(3)

print(double(5))  # 10
print(triple(5))  # 15

Built-in Examples

1. map, filter

# map takes function
squared = map(lambda x: x**2, [1, 2, 3])

# filter takes function
evens = filter(lambda x: x % 2 == 0, range(10))

Summary

• Take functions as args
• Return functions
• Enable abstraction
• Powerful pattern