Higher-Order Functions and Function Composition in Python with 10 Practical Examples

Higher-order functions and function composition are core concepts of functional programming that allow functions to be passed as arguments, returned as results, and combined to build more complex behavior.

Definition: A higher-order function is a function that takes one or more functions as parameters and/or returns a function.

Function as parameter example:

def apply_func(func, x):
    return func(x)

def square(x):
    return x ** 2

result = apply_func(square, 5)
print(result)  # 输出: 25

Function as return value example:

def create_adder(n):
    def adder(x):
        return x + n
    return adder

add_5 = create_adder(5)
result = add_5(3)
print(result)  # 输出: 8

Function composition example:

def add(x, y):
    return x + y

def square(x):
    return x ** 2

composed_func = lambda x: square(add(x, 5))
result = composed_func(3)
print(result)  # 输出: 64

Using map() for function mapping:

numbers = [1, 2, 3, 4, 5]

squared_numbers = list(map(lambda x: x ** 2, numbers))
print(squared_numbers)  # 输出: [1, 4, 9, 16, 25]

Using filter() for conditional filtering:

numbers = [1, 2, 3, 4, 5]

even_numbers = list(filter(lambda x: x % 2 == 0, numbers))
print(even_numbers)  # 输出: [2, 4]

Using reduce() for accumulation:

from functools import reduce

numbers = [1, 2, 3, 4, 5]

sum_of_numbers = reduce(lambda x, y: x + y, numbers)
print(sum_of_numbers)  # 输出: 15

Using list comprehensions for transformation and filtering:

numbers = [1, 2, 3, 4, 5]

squared_even_numbers = [x ** 2 for x in numbers if x % 2 == 0]
print(squared_even_numbers)  # 输出: [4, 16]

Using functools.partial() for function currying:

from functools import partial

def add(x, y):
    return x + y

add_5 = partial(add, 5)
result = add_5(3)
print(result)  # 输出: 8

These examples demonstrate common applications of higher-order functions and composition, helping you adopt a functional programming style in Python.