Programming in Python

Problem. Ask the user's name and age, greet them, and say how old they will be next year.

Solution.

name = input("Enter your name: ")
age = int(input("Enter your age: "))
print("Namaste,", name)
print("Next year you will be", age + 1)
print(f"{name} is {age} years old.")

Enter your name: Sujata
Enter your age: 15
Namaste, Sujata
Next year you will be 16
Sujata is 15 years old.

Without int(), age + 1 would fail, because age would be the text "15".

Problem. Predict, then check, the output.

Solution.

a = 17
b = 5
print(a + b, a - b, a * b)
print(a / b, a // b, a % b)
print(2 ** 10, 20 / 10)
print(-17 // 5, -17 % 5)
print(type(a), type(a / b), type("17"), type(a > b))

22 12 85
3.4 3 2
1024 2.0
-4 3
<class 'int'> <class 'float'> <class 'str'> <class 'bool'>

Problem. Read a percentage and print the SEE letter grade.

Solution.

marks = float(input("Enter percentage: "))
if marks >= 90:
    grade = "A+"
elif marks >= 80:
    grade = "A"
elif marks >= 70:
    grade = "B+"
elif marks >= 60:
    grade = "B"
elif marks >= 50:
    grade = "C+"
elif marks >= 40:
    grade = "C"
elif marks >= 35:
    grade = "D"
else:
    grade = "NG"
print("Grade:", grade)

Enter percentage: 86.5
Grade: A

With 33 the output is Grade: NG. Because the conditions are checked from the top, elif marks >= 80 is reached only when the mark is below 90.

Problem. Read an integer; print Positive, Negative or Zero, and for a positive number also print Even or Odd.

Solution.

n = int(input("Enter an integer: "))
if n > 0:
    print("Positive")
    if n % 2 == 0:
        print("Even")
    else:
        print("Odd")
elif n < 0:
    print("Negative")
else:
    print("Zero")

Three runs:

Enter an integer: 7
Positive
Odd

Enter an integer: -4
Negative

Enter an integer: 0
Zero

Problem. Print the multiplication table of a number up to 10.

Solution.

n = int(input("Enter a number: "))
for i in range(1, 11):
    print(n, "x", i, "=", n * i)

Enter a number: 7
7 x 1 = 7
7 x 2 = 14
7 x 3 = 21
7 x 4 = 28
7 x 5 = 35
7 x 6 = 42
7 x 7 = 49
7 x 8 = 56
7 x 9 = 63
7 x 10 = 70

Problem. Find the sum of the digits of a number and the number reversed.

Solution. num % 10 gives the last digit and num // 10 removes it.

num = int(input("Enter a number: "))
total = 0
rev = 0
while num > 0:
    digit = num % 10
    total = total + digit
    rev = rev * 10 + digit
    num = num // 10
print("Sum of digits:", total)
print("Reversed number:", rev)

Enter a number: 4521
Sum of digits: 12
Reversed number: 1254

Problem. Store five marks in a list, add a sixth, and print the count, total, highest, lowest, average and every distinction (80 or more).

Solution.

marks = [78, 92, 65, 88, 54]
print("Marks:", marks)
print("First:", marks[0], "Last:", marks[-1])
marks.append(81)
print("Number of marks:", len(marks))
print("Total:", sum(marks), "Highest:", max(marks), "Lowest:", min(marks))
print("Average:", round(sum(marks) / len(marks), 2))
for m in marks:
    if m >= 80:
        print(m, "is a distinction")

Marks: [78, 92, 65, 88, 54]
First: 78 Last: 54
Number of marks: 6
Total: 458 Highest: 92 Lowest: 54
Average: 76.33
92 is a distinction
88 is a distinction
81 is a distinction

Problem. Write a function that returns the sum of two numbers and call it.

Solution.

def add_numbers(x, y):
    total = x + y
    return total

num1 = 5
num2 = 6
print("The sum is", add_numbers(num1, num2))

The sum is 11

Python reads the def but runs nothing until the last line calls add_numbers(5, 6); the call is then replaced by the returned value, 11.

Problem. Write a simple-interest function whose rate is 10 % unless another rate is given, and call it three ways.

Solution.

def simple_interest(principal, time, rate=10):
    return principal * time * rate / 100

print(simple_interest(50000, 2))
print(simple_interest(50000, 2, 12))
print(simple_interest(rate=8, principal=20000, time=3))

10000.0
12000.0
4800.0

Problem. Write a function area_circle(r) that returns the area of a circle using 3.14 for π, and call it.

Solution.

def area_circle(r):
    return 3.14 * r * r

r = float(input("Enter radius: "))
print("Area =", area_circle(r))

Enter radius: 7
Area = 153.86

Problem. Return the square and cube of a number; then show what a void function returns.

Solution.

def square_and_cube(n):
    return n ** 2, n ** 3

result = square_and_cube(4)
print(result, type(result))
sq, cb = square_and_cube(5)
print("Square:", sq, "Cube:", cb)

def greet(name):
    print("Namaste,", name)

value = greet("Sita")
print("greet() returned:", value)

(16, 64) <class 'tuple'>
Square: 25 Cube: 125
Namaste, Sita
greet() returned: None

Problem. Predict the output.

Solution.

school = "Shree Janata Secondary School"    # global variable

def show():
    message = "Welcome to"                     # local variable
    print(message, school)

show()
print(school)
print(message)

Welcome to Shree Janata Secondary School
Shree Janata Secondary School
Traceback (most recent call last):
  File "scope.py", line 9, in <module>
    print(message)
          ^^^^^^^
NameError: name 'message' is not defined

The function can read the global school, but message disappeared when show() finished, so the last line fails. (Tracebacks in this chapter show only the file name; on your computer the full folder path appears.)

Problem. (a) Write is_prime(n) and test it on a few numbers. (b) Write a function that generates the series 2, 3, 5, 8, 13, … (each term the sum of the two before it) up to 10 terms and print the series and its sum.

Solution.

def is_prime(n):
    if n < 2:
        return False
    for i in range(2, int(n ** 0.5) + 1):
        if n % i == 0:
            return False
    return True

for number in [1, 2, 9, 17, 91, 97]:
    print(number, "is prime" if is_prime(number) else "is not prime")

def generate_series(n):
    series = [2, 3]
    for i in range(2, n):
        series.append(series[i - 1] + series[i - 2])
    return series

terms = generate_series(10)
print("Series:", *terms)
print("Sum of the series:", sum(terms))

1 is not prime
2 is prime
9 is not prime
17 is prime
91 is not prime
97 is prime
Series: 2 3 5 8 13 21 34 55 89 144
Sum of the series: 374

A divisor larger than √n would need a partner smaller than √n, so checking up to √n is enough. *terms prints the list's items separated by spaces.

Problem. Show each import style at work.

Solution.

from math import sqrt, pi
print(sqrt(25))
print(round(pi, 4))

import datetime as dt
print(dt.date(2082, 1, 1).year)

from math import *
print(sin(90))

5.0
3.1416
2082
0.8939966636005579

sin(90) is not 1: the trigonometric functions of math work in radians, and 90 radians is a different angle from 90°. Use sin(radians(90)) for degrees.

Problem. Use the math module for the calculations in the table.

Solution.

import math

print("Square root of 256:", math.sqrt(256))
print("2 to the power 10:", math.pow(2, 10))
print("pi =", math.pi)
print("Ceil of 4.2:", math.ceil(4.2), " Floor of 4.8:", math.floor(4.8))
print("5! =", math.factorial(5))
print("sin 30 degrees =", round(math.sin(math.radians(30)), 2))
print("log10(1000) =", math.log10(1000))
print("HCF of 84 and 120 =", math.gcd(84, 120))

Square root of 256: 16.0
2 to the power 10: 1024.0
pi = 3.141592653589793
Ceil of 4.2: 5  Floor of 4.8: 4
5! = 120
sin 30 degrees = 0.5
log10(1000) = 3.0
HCF of 84 and 120 = 12

Problem. Show each random function. Make the output repeatable so that it can be checked.

Solution. random.seed() fixes the starting point of the generator; the same seed always gives the same sequence. Remove the seed line and every run gives different numbers.

import random

random.seed(2083)
print(random.random())
print(random.randint(1, 6))
print(random.randrange(0, 100, 5))
print(random.choice(["Ram", "Sita", "Hari", "Gita"]))
cards = [1, 2, 3, 4, 5]
random.shuffle(cards)
print(cards)
print(random.sample(range(1, 51), 5))

0.9924157859181911
6
95
Ram
[5, 4, 2, 3, 1]
[4, 45, 12, 21, 10]

Problem. A student was born on 12 March 2010. On 14 April 2026 (1 Baisakh 2083 BS), how many days old is she and what is her age? What date is 100 days later?

Solution. Fixed dates are used so that the output can be checked; replace date(2026, 4, 14) with date.today() to use the real current date.

from datetime import date, datetime, timedelta

dob = date(2010, 3, 12)
today = date(2026, 4, 14)          # 1 Baisakh 2083 BS
print("Date of birth:", dob)
print("Year:", dob.year, "Month:", dob.month, "Day:", dob.day)
print(dob.strftime("%d %B %Y, a %A"))

age_days = (today - dob).days
print("Days lived:", age_days)
years = today.year - dob.year - ((today.month, today.day) < (dob.month, dob.day))
print("Age in years:", years)

later = today + timedelta(days=100)
print("100 days after New Year 2083:", later.strftime("%d-%m-%Y"))

moment = datetime(2026, 4, 14, 10, 30, 0)
print(moment.strftime("%I:%M %p on %d/%m/%Y"))

Date of birth: 2010-03-12
Year: 2010 Month: 3 Day: 12
12 March 2010, a Friday
Days lived: 5877
Age in years: 16
100 days after New Year 2083: 23-07-2026
10:30 AM on 14/04/2026

The comparison (today.month, today.day) < (dob.month, dob.day) is True (1) when this year's birthday has not yet come, so one year is subtracted. Python's datetime uses the AD calendar; Bikram Sambat dates need a separate converter.

Problem. Draw (a) a square of side 50, (b) a red triangle and a blue hexagon using one polygon() function, and (c) a red five-pointed star.

Solution.

(a)

import turtle
s = turtle.Turtle()
for i in range(4):
    s.forward(50)
    s.right(90)
turtle.done()

(b)

import turtle

def polygon(t, sides, length, colour):
    t.pencolor(colour)
    for i in range(sides):
        t.forward(length)
        t.left(360 / sides)

pen = turtle.Turtle()
pen.pensize(2)
polygon(pen, 3, 100, "red")
pen.penup()
pen.goto(150, 0)
pen.pendown()
polygon(pen, 6, 60, "blue")
turtle.done()

(c)

import turtle
t = turtle.Turtle()
t.color("red")
t.pensize(2)
for i in range(5):
    t.forward(150)
    t.right(144)
t.hideturtle()
turtle.done()

The outputs are the first three drawings of the figure below. Because (a) turns right, the square is drawn below the starting point; because (b) turns left, the triangle and hexagon are drawn above it.

Problem. Draw (a) a circle of radius and colour typed by the user, filled with that colour, (b) a dashed vertical line, and (c) a coloured square spiral.

Solution.

(a)

import turtle
t = turtle.Turtle()
r = int(input("Enter the radius of the circle: "))
col = input("Enter the colour name or hex value (#RRGGBB): ")
t.fillcolor(col)
t.begin_fill()
t.circle(r)
t.end_fill()
turtle.done()

(b)

import turtle
turtle.color("red")
turtle.hideturtle()
turtle.speed(1)
turtle.left(90)
for i in range(4):
    turtle.forward(30)
    turtle.penup()
    turtle.forward(30)
    turtle.pendown()
turtle.exitonclick()

(c)

import turtle
t = turtle.Turtle()
t.speed(0)
colours = ["red", "orange", "green", "blue"]
for i in range(40):
    t.pencolor(colours[i % 4])
    t.forward(i * 5)
    t.left(91)
t.hideturtle()
turtle.done()

For (a) the user typed 80 and orange. circle(80) actually draws a 25-sided polygon so close to a circle that the eye cannot tell. In (b) each pass draws 30 steps, lifts the pen for 30 steps and puts it down again, so four dashes appear. In (c) every line is 5 steps longer than the last and every turn is 91°, one degree more than a square, so each square is slightly rotated.

Problem. Divide two whole numbers typed by the user, handling non-numbers and division by zero, and always thank the user.

Solution.

try:
    a = int(input("Enter a number: "))
    b = int(input("Enter another number: "))
    result = a / b
except ValueError:
    print("Please enter whole numbers only.")
except ZeroDivisionError:
    print("A number cannot be divided by zero.")
else:
    print("Result:", result)
finally:
    print("Thank you for using the calculator.")

Three runs:

Enter a number: 20
Enter another number: 4
Result: 5.0
Thank you for using the calculator.

Enter a number: 20
Enter another number: 0
A number cannot be divided by zero.
Thank you for using the calculator.

Enter a number: twenty
Please enter whole numbers only.
Thank you for using the calculator.

Problem. Read marks between 0 and 100, asking again after any invalid entry.

Solution. A while True loop repeats until break is reached.

while True:
    try:
        marks = int(input("Enter marks (0-100): "))
        if 0 <= marks <= 100:
            break
        print("Marks must be between 0 and 100.")
    except ValueError:
        print("That is not a whole number. Try again.")
print("Marks accepted:", marks)

Enter marks (0-100): abc
That is not a whole number. Try again.
Enter marks (0-100): 150
Marks must be between 0 and 100.
Enter marks (0-100): 76
Marks accepted: 76

Problem. Create message.txt with two lines and display its contents.

Solution.

file = open("message.txt", "w")
file.write("Hello, welcome to file handling in Python!\n")
file.write("This is the second line.\n")
file.close()

file = open("message.txt", "r")
content = file.read()
print(content)
file.close()

Hello, welcome to file handling in Python!
This is the second line.

The blank last line appears because the file already ends with \n and print() adds one more.

Problem. (a) Store the name and class of three students in student.txt; (b) display the file; (c) append one more student and display it again.

Solution. Three separate programs.

(a)

file = open("student.txt", "w")
for i in range(3):
    name = input("Enter name of student: ")
    clas = input("Enter class of student: ")
    file.write(name + "," + clas + "\n")
file.close()
print("Data written to student.txt")

Enter name of student: Aarosh
Enter class of student: 10
Enter name of student: Nidhi
Enter class of student: 9
Enter name of student: Rajesh
Enter class of student: 10
Data written to student.txt

(b)

file = open("student.txt", "r")
print("Contents of student.txt:")
for line in file:
    print(line.strip())
file.close()

(c)

file = open("student.txt", "a")
name = input("Enter name of new student: ")
clas = input("Enter class of new student: ")
file.write(name + "," + clas + "\n")
file.close()
print("Data added to student.txt")

After appending Muna of Class 10, program (b) prints:

Contents of student.txt:
Aarosh,10
Nidhi,9
Rajesh,10
Muna,10

strip() removes the \n at the end of each line; without it every record would be followed by a blank line. The variable is called clas because class is a Python keyword.

Problem. Show what read(10), readline() and readlines() return one after another, and what happens with modes x and r.

Solution. The file remembers how far it has been read (the file pointer), so each method continues from where the last one stopped.

with open("student.txt", "r") as f:
    print(repr(f.read(10)))
    print(repr(f.readline()))
    print(f.readlines())
print("Closed?", f.closed)

try:
    f = open("student.txt", "x")
except FileExistsError:
    print("x mode: student.txt already exists, so it was not touched")
try:
    f = open("results.txt", "r")
except FileNotFoundError as e:
    print("r mode:", e)

'Aarosh,10\n'
'Nidhi,9\n'
['Rajesh,10\n', 'Muna,10\n']
Closed? True
x mode: student.txt already exists, so it was not touched
r mode: [Errno 2] No such file or directory: 'results.txt'

repr() shows the hidden \n characters. The first line happens to be exactly 10 characters long, so read(10) returns all of it.

Problem. Create students.csv with columns Name and Marks and three records, then display it.

Solution.

import csv

with open("students.csv", "w", newline="") as f:
    writer = csv.writer(f)
    writer.writerow(["Name", "Marks"])
    writer.writerows([["Aarosh", 78], ["Subigya", 92], ["Binay", 65]])
print("students.csv created")

with open("students.csv", "r") as f:
    reader = csv.reader(f)
    for row in reader:
        print(row)

students.csv created
['Name', 'Marks']
['Aarosh', '78']
['Subigya', '92']
['Binay', '65']

The csv module returns every value as a string ('78', not 78).

Problem. Make a DataFrame from a dictionary; then make one from a list of lists and save it as Stu_data.csv.

Solution.

import pandas as pd

data = {"Name": ["Shyam", "Sanskar"], "Age": [25, 30]}
df = pd.DataFrame(data)
print(df)

header = ["Name", "M1 Score", "M2 Score"]
rows = [["Sanskar", 62, 80], ["Sambriddhi", 45, 56], ["Aurora", 85, 98]]
scores = pd.DataFrame(rows, columns=header)
scores.to_csv("Stu_data.csv", index=False)
print(open("Stu_data.csv").read())

      Name  Age
0    Shyam   25
1  Sanskar   30
Name,M1 Score,M2 Score
Sanskar,62,80
Sambriddhi,45,56
Aurora,85,98

The numbers 0 and 1 at the left are the index. index=False keeps it out of the CSV file.

Problem. Read result.csv; show the first five rows, its size, its column names and the average Computer mark; list the boys who scored more than 85 in Computer; add a Total column and show the top three.

Solution.

import pandas as pd

df = pd.read_csv("result.csv")
print(df.head())
print("Shape:", df.shape)
print("Columns:", list(df.columns))
print("Average in Computer:", df["Computer"].mean())

boys = df[(df["Gender"] == "M") & (df["Computer"] > 85)]
print(boys[["Name", "Computer"]])

df["Total"] = df["English"] + df["Nepali"] + df["Maths"] + df["Computer"]
top = df.sort_values("Total", ascending=False)
print(top[["Name", "Total"]].head(3))

   Symbol No     Name Gender  English  Nepali  Maths  Computer
0       1001   Aarosh      M       72      68     81        88
1       1002  Subigya      F       85      79     90        94
2       1003    Binay      M       64      70     58        91
3       1004    Nidhi      F       78      82     75        86
4       1005     Aman      M       55      61     49        72
Shape: (8, 7)
Columns: ['Symbol No', 'Name', 'Gender', 'English', 'Nepali', 'Maths', 'Computer']
Average in Computer: 86.375
     Name  Computer
0  Aarosh        88
2   Binay        91
      Name  Total
5   Anjali    367
1  Subigya    348
6   Rajesh    325

Problem. employee.csv stores Name, Address, Gender and Salary. Show the employees who earn more than 75,000, and count those earning more than 50,000.

Solution.

import pandas as pd

df = pd.read_csv("employee.csv")
print("Employees with salary more than 75,000:")
print(df[df["Salary"] > 75000])
print("Employees with salary more than 50,000:", len(df[df["Salary"] > 50000]))

With six employees in the file, the output was:

Employees with salary more than 75,000:
           Name    Address Gender  Salary
0    Hari Thapa  Kathmandu      M   82000
3  Laxmi Gurung    Pokhara      F   91000
5    Anita Shah    Birgunj      F   77500
Employees with salary more than 50,000: 5

Problem. Draw a line chart of Nepal's population at the last five censuses: 15.02, 18.49, 23.15, 26.49 and 29.16 million in 1981, 1991, 2001, 2011 and 2021.

Solution.

import matplotlib.pyplot as plt

years = [1981, 1991, 2001, 2011, 2021]
population = [15.02, 18.49, 23.15, 26.49, 29.16]   # millions, from the census

plt.plot(years, population, marker="o")
plt.title("Population of Nepal by census")
plt.xlabel("Census year")
plt.ylabel("Population (millions)")
plt.grid(True)
plt.show()

marker="o" puts a dot on each data point and plt.grid(True) adds grid lines. The chart shows the population rising every decade, but more slowly after 2001: the line bends.

Problem. Read result.csv with pandas and draw a bar chart of the class average in each subject.

Solution.

import pandas as pd
import matplotlib.pyplot as plt

df = pd.read_csv("result.csv")
subjects = ["English", "Nepali", "Maths", "Computer"]
averages = [df[s].mean() for s in subjects]
for s, a in zip(subjects, averages):
    print(s, round(a, 2))

plt.bar(subjects, averages, color="green")
plt.title("Average marks of the class")
plt.xlabel("Subject")
plt.ylabel("Average marks")
plt.show()

English 74.25
Nepali 74.88
Maths 74.25
Computer 86.38

Problem. Of 40 students, 18 walk to school, 12 come by school bus, 6 by bicycle and 4 by motorbike. Draw a pie chart with percentages.

Solution.

import matplotlib.pyplot as plt

modes = ["Walk", "School bus", "Bicycle", "Motorbike"]
students = [18, 12, 6, 4]

plt.pie(students, labels=modes, autopct="%1.1f%%", startangle=90)
plt.title("How 40 students come to school")
plt.show()

autopct="%1.1f%%" writes each slice's percentage with one decimal place (18 ÷ 40 = 45.0 %), and startangle=90 starts the first slice at the top.

Problem. Plot the marks of eight students against their daily hours of study: hours 1, 2, 2.5, 3, 4, 4.5, 5, 6 and marks 45, 52, 58, 61, 70, 74, 79, 88.

Solution.

import matplotlib.pyplot as plt

hours = [1, 2, 2.5, 3, 4, 4.5, 5, 6]
marks = [45, 52, 58, 61, 70, 74, 79, 88]

plt.scatter(hours, marks, color="red")
plt.title("Study hours and marks")
plt.xlabel("Hours of study per day")
plt.ylabel("Marks")
plt.show()

The dots rise from left to right: in this group, more study goes with higher marks.