Small anonymous functions plus map, filter, sorted(key=…) and functools — Python's functional toolkit.

lambda

lambda args: expression — a one-expression function with no name, no statements and no annotations. Best as a short key= or callback.

Python

add = lambda a, b: a + b
print(add(2, 3))                                            # 5
words = ["banana", "Apple", "cherry"]
print(sorted(words, key=str.lower))                         # ['Apple', 'banana', 'cherry']
print(sorted(words, key=lambda w: (len(w), w)))             # ['Apple', 'banana', 'cherry']
print(max(["aa", "b", "cccc"], key=len))                    # cccc

map, filter, zip

Python

nums = [1, 2, 3, 4]
print(list(map(lambda x: x * 10, nums)))        # [10, 20, 30, 40]
print(list(filter(lambda x: x % 2, nums)))      # [1, 3]
print(list(map(int, "123")))                    # [1, 2, 3]
print(list(map(pow, [2, 3], [3, 2])))           # [8, 9]

functools

Python

from functools import reduce, partial, cache, lru_cache

print(reduce(lambda acc, x: acc * x, [1, 2, 3, 4], 1))   # 24

base2 = partial(int, base=2)
print(base2("1011"))                                      # 11

@cache
def fib(n):
    return n if n < 2 else fib(n - 1) + fib(n - 2)
print(fib(80))                                            # 23416728348467685

@lru_cache(maxsize=128)
def slow_square(x):
    return x * x
slow_square(4); slow_square(4)
print(slow_square.cache_info().hits)                      # 1

Python

from operator import itemgetter
rows = [("b", 2), ("a", 3), ("c", 1)]
print(sorted(rows, key=itemgetter(1)))    # [('c', 1), ('b', 2), ('a', 3)]