Modules and the standard library

You don't have to write code from scratch to take a square root, pick a random number or count the days between two dates. Python comes with a standard library full of ready-made tools. These tools are grouped into modules — you simply load the one you need and use it.

import and the math module

import math

print(math.sqrt(144))
print(math.pi)
print(math.ceil(4.2), math.floor(4.8))
print(math.gcd(24, 36))

12.0
3.141592653589793
5 4
12

ceil rounds a number up, floor rounds it down, and gcd finds the greatest common divisor of two numbers. If you only need a few names from a module, you can take them directly with from ... import — then you don't need to write math. any more:

from math import sqrt, pi

radius = 3
area = pi * radius ** 2
print(f'Circle area: {area:.2f}')
print(sqrt(2))

Circle area: 28.27
1.4142135623730951

random: random numbers

Games, quizzes and tests need randomness. The most used functions of the random module are: randint(a, b) — a random whole number from a to b (both included), choice(list) — a random item from a list, and shuffle(list) — mixing up a list.

import random

for i in range(3):
    print(f'Roll {i + 1}: {random.randint(1, 6)}')

Sometimes you need to repeat random results — for example, when testing a program. random.seed() sets the starting point of the sequence: with the same seed, the “random” values come out the same every time.

import random

random.seed(42)
print(random.randint(1, 6))
print(random.choice(['rock', 'paper', 'scissors']))
cards = [1, 2, 3, 4, 5]
random.shuffle(cards)
print(cards)

6
rock
[2, 4, 5, 3, 1]

datetime: dates and times

In Azerbaijan the school year starts on 15 September — Knowledge Day. How many days are there from that day to New Year? In the datetime module, date represents a date and timedelta a length of time. Subtracting one date from another gives a timedelta, and its days attribute holds the number of days.

from datetime import date, timedelta

start = date(2026, 9, 15)
new_year = date(2027, 1, 1)
print(start)
print(start.strftime('%d.%m.%Y'))
print((new_year - start).days, 'days until New Year')
print(start + timedelta(days=100))

2026-09-15
15.09.2026
108 days until New Year
2026-12-24

strftime turns a date into a string in any format you like: %d means day, %m month and %Y year. date.today() gives today's date — so the result of the code below is different every day:

from datetime import date

today = date.today()
print('Today is', today.strftime('%d.%m.%Y'))
print('Days left this year:', (date(today.year, 12, 31) - today).days)

What else is in the standard library?

import statistics
from collections import Counter

scores = [7, 9, 6, 9, 10, 8, 9]
print(round(statistics.mean(scores), 2))
print(statistics.median(scores))

votes = ['pizza', 'plov', 'plov', 'dolma', 'plov', 'pizza']
print(Counter(votes).most_common(2))

8.29
9
[('plov', 3), ('pizza', 2)]

pupils = 95
seats = 40
radius = 3.5
# 1) import math
# 2) print how many buses are needed
# 3) print the area of the pool with 2 digits after the point

3
38.48

grades = [5, 4, 5, 3, 5, 4, 2, 5]
# 1) import mean, median and Counter
# 2) print the mean and the median
# 3) print the most common grade like: Most common: 3 (2 times)

4.125
4.5
Most common: 5 (4 times)