Lambda Functions and Higher-Order Functions

Anonymous functions, map(), filter(), sorted(), and functional programming basics.

Lambda Functions

A lambda is an anonymous single-expression function. Useful for short, throwaway operations:

square = lambda x: x ** 2
print(square(6))   # 36

add = lambda a, b: a + b
print(add(3, 5))   # 8

map()

Apply a function to every item in an iterable:

nums = [1, 2, 3, 4, 5]
squares = list(map(lambda x: x**2, nums))
print(squares)   # [1, 4, 9, 16, 25]

filter()

Keep only items for which the function returns True:

evens = list(filter(lambda x: x % 2 == 0, nums))
print(evens)   # [2, 4]

sorted() with a Key

words = ["banana", "apple", "cherry", "kiwi"]
# sort by length
by_len = sorted(words, key=lambda w: len(w))
print(by_len)   # ['kiwi', 'apple', 'banana', 'cherry']

reduce() from functools

from functools import reduce
product = reduce(lambda x, y: x * y, [1, 2, 3, 4, 5])
print(product)   # 120