Python map(), filter(), reduce() — Functional Essentials

map(fn, iterable)

nums = [1, 2, 3, 4]
squared = list(map(lambda n: n*n, nums))
# [1, 4, 9, 16]

filter(fn, iterable)

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

functools.reduce(fn, iterable)

from functools import reduce
total = reduce(lambda a, b: a + b, nums)   # 10
prod  = reduce(lambda a, b: a * b, nums)   # 24

List Comprehension Alternatives

For readability, many Python programmers prefer comprehensions:

squared = [n*n for n in nums]
evens   = [n for n in nums if n % 2 == 0]

When Each Wins

• map/filter — short, reusing an existing function.
• comprehension — readable, multiple conditions, transformations.
• reduce — sums, products, custom aggregation.