Functional Programming in Python

map() — apply function to every item:

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

# Prefer list comprehension:
squares = [x**2 for x in numbers]

filter() — keep items matching condition:

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

# Prefer:
evens = [x for x in numbers if x % 2 == 0]

reduce() — aggregate to single value:

from functools import reduce
total = reduce(lambda a, b: a + b, numbers)  # 15
# Prefer: sum(numbers)

functools.lru_cache — memoization:

from functools import lru_cache

@lru_cache(maxsize=None)
def fibonacci(n):
    if n < 2:
        return n
    return fibonacci(n-1) + fibonacci(n-2)

fibonacci(100)  # instant, not exponential

partial — pre-fill function arguments:

from functools import partial
double = partial(lambda x, n: x * n, n=2)
double(5)  # 10

Reference:

Wikipedia: Functional Programming

https://en.wikipedia.org/wiki/Functional_programming