Practice: Standard Library Essentials¶

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Four practice problems, one per concept step. The numbers line up. Build each yourself, then check python-practice/solutions. Some end with a short input() "Write a Program" exercise.

These problems continue one connected story: you are writing the store reporting tools for an online store. The math module does the number-crunching on totals, random picks the day's order count, the featured product and a fresh homepage order, datetime stamps order ship and arrival dates, and collections.Counter finds the best sellers.

Step-01: Import a Module and Use math¶

Concepts: import, math.sqrt, math.ceil, math.floor, math.pi, statistics.mean, input().

Problem-1: Store Report Numbers.

Write a program that, using the math module, prints these labeled lines:

• Task-1: the square root of 169 (use math.sqrt).
• Task-2: the rounded-up box count for 7.2 (use math.ceil).
• Task-3: the rounded-down full-pallet count for 5.8 (use math.floor).
• Task-4: the value of pi (use math.pi).

square root of 169 is: 13.0
rounded-up boxes for 7.2 is: 8
rounded-down full pallets for 5.8 is: 5
pi is about: 3.141592653589793

import math

# Problem-1 Task-1: print square root of 169
print("square root of 169 is:", math.sqrt(169))
# Problem-1 Task-2: print rounded-up boxes for 7.2
print("rounded-up boxes for 7.2 is:", math.ceil(7.2))
# Problem-1 Task-3: print rounded-down pallets for 5.8
print("rounded-down full pallets for 5.8 is:", math.floor(5.8))
# Problem-1 Task-4: print the value of pi
print("pi is about:", math.pi)

Problem-2: Average Order Total. Write a program that prints a labeled line with the mean (average) of the order totals 120, 80, and 250, using the statistics module (use statistics.mean).

average order total: 150

import statistics

# Problem-2 Task-1: print mean of the order totals
print("average order total:", statistics.mean([120, 80, 250]))

Problem-3 (Write a Program): Order Total Check. Write a program that asks the user for an order total and prints its square root.

Enter an order total: 400
square root: 20.0

import math

# Problem-3 Task-1: read order total and print its square root
order_total = int(input("Enter an order total: "))
print("square root:", math.sqrt(order_total))

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Step-02: Random Values with random¶

Concepts: random.seed, randint, choice, shuffle.

Problem-1: Featured Product Picker.

Write a program that seeds random with 5 (use random.seed) so the output repeats, then prints these labeled lines:

• Task-1: the number of orders today, a whole number from 50 to 150 (use random.randint).
• Task-2: one featured product picked at random (use random.choice) from the list Laptop, Headphones, Keyboard, Monitor.
• Task-3: the list Laptop, Headphones, Keyboard, Monitor shuffled in place for a fresh homepage order (use random.shuffle).

Expected output (with seed 5):

orders today: 129
featured product: Keyboard
homepage order: ['Headphones', 'Laptop', 'Monitor', 'Keyboard']

import random

random.seed(5)

# Task-1: print random order count from 50 to 150
print("orders today:", random.randint(50, 150))

# Task-2: pick and print one featured product
featured_products = ["Laptop", "Headphones", "Keyboard", "Monitor"]
print("featured product:", random.choice(featured_products))

# Task-3: shuffle the list and print homepage order
homepage_lineup = ["Laptop", "Headphones", "Keyboard", "Monitor"]
random.shuffle(homepage_lineup)
print("homepage order:", homepage_lineup)

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Step-03: Dates with datetime¶

Concepts: datetime(y, m, d), strftime, strptime, reading parts, timedelta.

Problem-1: Ship and Arrival Dates.

Write a program that builds a datetime ship_date for 5 March 2026 and an arrival_date 5 days after it (add a timedelta of 5 days), then prints these labeled lines:

• Task-1: ship_date formatted as %d %B %Y (use strftime).
• Task-2: the month of ship_date (use .month).
• Task-3: arrival_date formatted as %d %B %Y (use strftime).
• Task-4: the days in transit: subtract ship_date from arrival_date and read .days.

ship date: 05 March 2026
month: 3
arrival date: 10 March 2026
days in transit: 5

from datetime import datetime, timedelta

ship_date = datetime(2026, 3, 5)

# Problem-1 Task-1: print ship_date formatted as day month year
print("ship date:", ship_date.strftime("%d %B %Y"))
# Problem-1 Task-2: print the month of ship_date
print("month:", ship_date.month)

arrival_date = ship_date + timedelta(days=5)
# Problem-1 Task-3: print arrival_date formatted as day month year
print("arrival date:", arrival_date.strftime("%d %B %Y"))
# Problem-1 Task-4: print the days in transit (arrival_date minus ship_date, read .days)
days_in_transit = arrival_date - ship_date
print("days in transit:", days_in_transit.days)

Problem-2: Sale Day From Text.

Write a program that parses the text "2026-11-27" (the store's sale day) into a date (use datetime.strptime with the format "%Y-%m-%d"), then prints these labeled lines:

• Task-1: the parsed date formatted as %d %B %Y (use strftime).
• Task-2: the year of the parsed date (use .year).

sale day: 27 November 2026
year: 2026

sale_day = datetime.strptime("2026-11-27", "%Y-%m-%d")
# Problem-2 Task-1: print the parsed date formatted as day month year
print("sale day:", sale_day.strftime("%d %B %Y"))
# Problem-2 Task-2: print the year of the parsed date
print("year:", sale_day.year)

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Step-04: Count Items with collections.Counter¶

Concepts: Counter, most_common, input().

Problem (Write a Program): Best-Selling Letter.

Write a program that asks the user for a product name, then prints these labeled lines:

• Task-1: how many times each letter appears in the product name (use Counter).
• Task-2: the single most frequent letter (use most_common(1)).
• Task-3: the count of the letter z in the name (index the Counter with "z"). A Counter returns 0 for a letter that is not there, instead of raising an error.

Enter a product name: sensors
letter counts: Counter({'s': 3, 'e': 1, 'n': 1, 'o': 1, 'r': 1})
most common: [('s', 3)]
count of z: 0

from collections import Counter

product_name = input("Enter a product name: ")

# Task-1: count and print how many times each letter appears
letter_tally = Counter(product_name)
print("letter counts:", letter_tally)
# Task-2: print the single most frequent letter
print("most common:", letter_tally.most_common(1))
# Task-3: a Counter returns 0 for a letter that never appeared, instead of an error
print("count of z:", letter_tally["z"])

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