A Tour of the Standard Library

Python ships with a huge toolbox so you rarely start from scratch. Here are four modules you will reach for constantly.

datetime

from datetime import date

d = date(2026, 6, 17)
print(d.year)        # 2026
print(d.isoformat()) # 2026-06-17

math

import math
print(math.sqrt(144))   # 12.0
print(math.floor(3.7))  # 3
print(math.pi)          # 3.1415...

random (seed it for repeatable results)

Random output changes each run, which is bad for tests. Call random.seed(n) first to make the sequence deterministic, so the same seed always gives the same numbers.

import random
random.seed(42)
print(random.randint(1, 6))  # same value every run with seed 42

collections.Counter

Counter tallies how often each item appears, returning a dict-like object:

from collections import Counter
tally = Counter("banana")
print(tally["a"])          # 3
print(tally.most_common(1)) # [('a', 3)]