Brief Overview of Python

Overview

Learning outcomes

• Students will be able to run Python statements in interactive mode and write, save and run programs in script mode.
• Students will be able to identify keywords and frame valid identifiers and variables following Python's rules.
• Students will be able to name Python's data types and classify them as mutable or immutable.
• Students will be able to use arithmetic, relational, logical, assignment, membership and identity operators and evaluate expressions using operator precedence.
• Students will be able to accept input, display formatted output and convert values between data types.
• Students will be able to distinguish syntax, logical and runtime errors and debug simple programs.
• Students will be able to write programs using if, if-else and if-elif-else statements.
• Students will be able to write programs using while loops, for loops with range(), and nested loops.

Lesson plan

Notes

print("Welcome to Informatics Practices")
print("Class XI, Session 2025-26")

Welcome to Informatics Practices
Class XI, Session 2025-26

>>> 25 + 17
42
>>> runs = 48
>>> runs * 2
96
>>> runs
48
>>> "Virat " + "Kohli"
'Virat Kohli'

# Program: check result of a student
marks = 72                 # statement
if marks >= 33:            # header line ends with a colon
    print("Result: Pass")  # indented block (4 spaces)
    print("Well done!")
else:
    print("Result: Fail")
print("Thank you")         # not indented: runs in every case

Result: Pass
Well done!
Thank you

import keyword
print(keyword.kwlist)
print(len(keyword.kwlist), "keywords")

['False', 'None', 'True', 'and', 'as', 'assert', 'async', 'await', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield']
35 keywords

PI = 3.14159              # constant by convention
radius = 7
area = PI * radius * radius
print("Area:", area)
a, b = 15, 40
a, b = b, a               # swap
print("a =", a, "b =", b)
x = y = z = 0
print(x, y, z)
city = "Jaipur"           # same name can later hold another type
print(type(radius), type(city))

Area: 153.93791
a = 40 b = 15
0 0 0
<class 'int'> <class 'str'>

values = [45, 99.5, 2+3j, True, "Kolkata", [1, 2], (5, 6), {"roll": 1}, None]
for v in values:
    print(repr(v), "->", type(v))

45 -> <class 'int'>
99.5 -> <class 'float'>
(2+3j) -> <class 'complex'>
True -> <class 'bool'>
'Kolkata' -> <class 'str'>
[1, 2] -> <class 'list'>
(5, 6) -> <class 'tuple'>
{'roll': 1} -> <class 'dict'>
None -> <class 'NoneType'>

marks = [80, 75, 90]
old_id = id(marks)
marks[1] = 78                     # change in place
print(marks, "same object:", id(marks) == old_id)

city = "Delhi"
old_id = id(city)
city = city + " NCR"              # new string object is created
print(city, "same object:", id(city) == old_id)

name = "ravi"
name[0] = "R"                     # strings are immutable

[80, 78, 90] same object: True
Delhi NCR same object: False
TypeError: 'str' object does not support item assignment

print(17 + 4, 17 - 4, 17 * 4, 17 / 4)
print(17 // 4, 17 % 4, 2 ** 5)
print(10 / 2, -17 // 4, -17 % 4, 17.0 // 4)
print("Ha" * 3, "Raj" + "kot")

21 13 68 4.25
4 1 32
5.0 -5 3 4.0
HaHaHa Rajkot

marks, attendance = 68, 72
print(marks >= 33, marks == 100, "Apple" < "apple", 0 <= marks <= 100)
print(marks >= 33 and attendance >= 75)
print(marks >= 33 or attendance >= 75)
print(not attendance >= 75)
total = 100
total += 25
total //= 2
print(total)
print(bool(0), bool(""), bool("0"), bool([]))

True False True True
False
True
True
62
False False True False

vowels = "aeiou"
print("e" in vowels, "z" not in vowels)
teams = ["CSK", "MI", "RCB"]
print("MI" in teams, "KKR" in teams)
list1 = [1, 2, 3]
list2 = [1, 2, 3]
list3 = list1
print(list1 == list2, list1 is list2, list1 is list3)

True True
True False
True False True

print(12 + 3 * 4 ** 2 // 5 - 1)
print(2 ** 3 ** 2, (2 ** 3) ** 2)
print(-3 ** 2, (-3) ** 2)
print(20 - 8 - 4, 30 / 5 * 3)
print(not 5 > 3 or 2 < 1)
print(10 > 5 and 3 > 4 or 7 > 2)

20
512 64
-9 9
8 18.0
False
True

a, b = 15, 4
print(a / b + (a % b) * 2)       # 3.75 + 3*2
print(a // b + 2.0)              # int + float -> float
print(15.0 / 4.0 + (8 + 3.0))
print(a > b and a % b == 3)

9.75
5.0
14.75
True

"""
Program : Electricity bill
Author  : Class XI-B
"""
units = 150            # units consumed this month
rate = 6.5             # rupees per unit
# bill is units multiplied by rate
print("Bill amount: Rs", units * rate)

Bill amount: Rs 975.0

name = input("Enter your name: ")
age = int(input("Enter your age: "))
print("Hello", name)
print("Next year you will be", age + 1)
print(28, 10, 2026, sep="/")
print("Loading", end="...")
print("done")

Enter your name: Meera
Enter your age: 16
Hello Meera
Next year you will be 17
28/10/2026
Loading...done

print(5 + 2.5, True + 3)          # implicit
print(int("45") + 5, int(9.99), int(-9.99))
print(float("3.5") * 2, float(7))
print("Score: " + str(100) + "%")
print(round(1234.5678, 2), round(7.5))
print(int("12.5"))

7.5 4
50 9 -9
7.0 7.0
Score: 100%
1234.57 8
ValueError: invalid literal for int() with base 10: '12.5'

a, b = 60, 80
avg = a + b / 2              # logical error: runs, but wrong
print("Wrong average:", avg)
avg = (a + b) / 2            # corrected
print("Correct average:", avg)
students = 0
print("Per student:", 500 / students)   # runtime error

Wrong average: 100.0
Correct average: 70.0
ZeroDivisionError: division by zero

import math
print(abs(-25), max(12, 45, 7), min(12, 45, 7))
print(math.sqrt(144), math.ceil(4.1), math.floor(4.9))
print(round(math.pi * 7 * 7, 2))

25 45 7
12.0 5 4
153.94

percent = 78.5
if percent >= 90:
    grade = "A1"
elif percent >= 75:
    grade = "A2"
elif percent >= 60:
    grade = "B"
elif percent >= 33:
    grade = "C"
else:
    grade = "Fail"
print("Grade:", grade)

age = 17
if age >= 18:
    print("Eligible to vote")
else:
    print("Wait", 18 - age, "year(s) to vote")

Grade: A2
Wait 1 year(s) to vote

count = 1                     # initialise
while count <= 5:             # test
    print(count, end=" ")
    count += 1                # update
print()

num = 4725
digit_sum = 0
reverse = 0
while num > 0:
    digit = num % 10
    digit_sum += digit
    reverse = reverse * 10 + digit
    num //= 10
print("Sum of digits:", digit_sum, "Reverse:", reverse)

1 2 3 4 5 
Sum of digits: 18 Reverse: 5274

for ch in "INDIA":
    print(ch, end=" ")
print()
for n in range(10, 0, -2):
    print(n, end=" ")
print()
print(list(range(1, 10, 3)), list(range(5, 1)))
total = 0
for i in range(1, 11):
    total += i
print("Sum of 1 to 10 =", total)

I N D I A 
10 8 6 4 2 
[1, 4, 7] []
Sum of 1 to 10 = 55

for row in range(1, 5):
    for col in range(1, row + 1):
        print(col, end=" ")
    print()                      # new line after each row

for i in range(2, 4):
    for j in range(1, 4):
        print(i, "x", j, "=", i * j, end="   ")
    print()

1 
1 2 
1 2 3 
1 2 3 4 
2 x 1 = 2   2 x 2 = 4   2 x 3 = 6   
3 x 1 = 3   3 x 2 = 6   3 x 3 = 9

for n in range(1, 11):
    if n % 3 == 0:
        continue          # skip multiples of 3
    if n > 8:
        break             # stop the loop
    print(n, end=" ")

1 2 4 5 7 8

Key terms

Interpreter

Software that translates and executes a program one statement at a time.

Interactive mode

Running Python statements one at a time at the >>> prompt; code is not saved.

Script mode

Writing a program in a .py file, saving it and running it as a whole.

Keyword

A reserved word with a special meaning that cannot be used as an identifier.

Identifier

A name given to a variable, function or other object in a program.

Variable

A name that refers to a value stored in memory.

Literal

A fixed value written directly in code, such as 25, 3.5 or "Pune".

Constant

A value that does not change during the program; by convention written in capitals.

Data type

The kind of value (int, float, str, list, etc.) that decides which operations are allowed.

Mutable

A type whose value can be changed in place, such as list and dict.

Immutable

A type whose value cannot be changed in place, such as int, float, str and tuple.

Operator

A symbol that performs an operation on one or more operands.

Precedence

The order in which operators in an expression are applied.

Expression

A combination of values, variables and operators that evaluates to a single value.

Statement

A complete instruction that the interpreter can execute.

Indentation

Spaces at the start of a line that mark a block of code in Python.

Comment

Text after # (or in an unassigned triple-quoted string) that the interpreter ignores.

Type conversion

Changing a value from one data type to another, implicitly or explicitly.

Debugging

The process of finding and removing errors from a program.

Infinite loop

A loop whose condition never becomes False, so it never ends.

MCQs

Tap an option to check it, or use Show answers above to reveal them all.

1. Which of the following is a valid identifier in Python?

   1. 2nd_term
   2. total-marks
   3. _roll_no
   4. for
   Answer

   (c) _roll_no

   An identifier may start with an underscore. 2nd_term starts with a digit, total-marks has a hyphen and for is a keyword.

2. In which mode does Python display the value of an expression without using print()?

   1. Interactive mode
   2. Script mode
   3. Both modes
   4. Neither mode
   Answer

   (a) Interactive mode

   At the >>> prompt the value of a bare expression is echoed automatically. In script mode, print() is needed.

3. Which of these is not a keyword in Python?

   1. None
   2. elif
   3. print
   4. pass
   Answer

   (c) print

   print is a built-in function, not a keyword. None, elif and pass are keywords.

4. What is the output of the following code?

   print(23 // 4, 23 % 4)

   1. 5 1
   2. 5.75 1
   3. 5 3
   4. 5.0 3
   Answer

   (c) 5 3

   23 // 4 gives the quotient 5 and 23 % 4 gives the remainder 3.

5. What is the output of the following code?

   print(2 ** 3 ** 2)

   1. 64
   2. Error
   3. 4096
   4. 512
   Answer

   (d) 512

   ** is right-associative: 2 ** 3 ** 2 is 2 ** 9 = 512.

6. Which data type is mutable?

   1. tuple
   2. list
   3. str
   4. int
   Answer

   (b) list

   Lists can be changed in place; the other three are immutable.

7. What will type(5 / 5) return?

   print(type(5 / 5))

   1. <class 'int'>
   2. <class 'str'>
   3. <class 'bool'>
   4. <class 'float'>
   Answer

   (d) <class 'float'>

   The / operator always returns a float, even when the division is exact (1.0).

8. What is the output of the following code?

   print(-4 ** 2)

   1. 16
   2. -16
   3. 4
   4. -8
   Answer

   (b) -16

   ** has higher precedence than unary minus, so it is -(4 ** 2) = -16.

9. What does int("7.9") produce?

   1. 7
   2. 8
   3. 7.9
   4. ValueError
   Answer

   (d) ValueError

   int() cannot convert a string that contains a decimal point. int(7.9) (a float, without quotes) would give 7.

10. What is the output of the following code?

    a, b = 10, 20
    print(a < b and b < a or a == b)

    1. TrueFalse
    2. True
    3. False
    4. Error
    Answer

    (c) False

    and is applied before or: (True and False) or False = False or False = False.

11. Which error occurs when a program divides a number by zero?

    1. ZeroDivisionError
    2. SyntaxError
    3. NameError
    4. Logical error
    Answer

    (a) ZeroDivisionError

    Division by zero is detected only while running, so it is a runtime error named ZeroDivisionError.

12. A program to find the average of three numbers runs without any message but prints a wrong answer. This is a:

    1. Syntax error
    2. Runtime error
    3. Logical error
    4. Indentation error
    Answer

    (c) Logical error

    The program runs fully but the logic (formula) is wrong, which is a logical error.

13. What is the output of the following code?

    for i in range(2, 10, 2):
        print(i, end=" ")

    1. 2 4 6 8 10
    2. 2 4 6 8 10 12
    3. 2 5 8
    4. 2 4 6 8
    Answer

    (d) 2 4 6 8

    range(2, 10, 2) produces 2, 4, 6, 8; the stop value 10 is excluded.

14. How many times will the following loop run?

    x = 20
    count = 0
    while x > 0:
        x -= 5
        count += 1
    print(count)

    1. 4
    2. 5
    3. 6
    4. Infinite
    Answer

    (a) 4

    x takes the values 20, 15, 10, 5. When x becomes 0 the condition fails, so the body runs 4 times.

15. Which symbol is used to write a single-line comment in Python?

    1. //
    2. #
    3. /*
    4. --
    Answer

    (b) #

    Everything after # on a line is a comment.

16. What is the output of the following code?

    m = 65
    if m >= 75:
        print("Merit")
    elif m >= 33:
        print("Pass")
    else:
        print("Fail")

    1. Pass
    2. Merit
    3. PassMerit
    4. Fail
    Answer

    (a) Pass

    65 >= 75 is False, so Python checks the elif: 65 >= 33 is True, so "Pass" is printed and the rest of the ladder is skipped.

17. What is the output of print("5" * 3)?

    print("5" * 3)

    1. 555
    2. 15
    3. 5 5 5
    4. Error
    Answer

    (a) 555

    * with a string and an integer repeats the string.

18. Which statement about input() is correct?

    1. It returns an int when a number is typed
    2. It always returns a string
    3. It returns a float for decimal numbers
    4. It cannot show a message
    Answer

    (b) It always returns a string

    input() returns whatever is typed as a string; it must be converted with int() or float() for calculations.

19. What is the output of the following code?

    p = [1, 2]
    q = [1, 2]
    print(p == q, p is q)

    1. True True
    2. False False
    3. False True
    4. True False
    Answer

    (d) True False

    == compares values (equal), while is checks whether both names refer to the same object (they are two different lists).

20. Which of the following is evaluated first in 8 + 6 / 3 * 2 - 1?

    1. 8 + 6
    2. 6 / 3
    3. 3 * 2
    4. 2 - 1
    Answer

    (b) 6 / 3

    / and * share a level higher than + and -, and they are applied left to right, so 6 / 3 is done first. The value is 11.0.

Assertion–Reason

1. Assertion (A): In Python, 10 / 5 gives the value 2.0.

   Reason (R): The / operator always returns a floating-point result.

   Answer

   (A)

   Both are true and R explains why the result is 2.0 and not 2.

2. Assertion (A): A string can be used where Python expects an immutable value.

   Reason (R): After a string is created, its individual characters can be changed using an index.

   Answer

   (C)

   Strings are immutable, so A is true. R is false: s[0] = "x" raises a TypeError.

3. Assertion (A): total_2025 is a valid identifier.

   Reason (R): An identifier can contain digits, but it cannot begin with one.

   Answer

   (A)

   Both are true and R is the rule that makes total_2025 valid (it begins with a letter).

4. Assertion (A): range(1, 5) produces the numbers 1, 2, 3, 4 and 5.

   Reason (R): The stop value given to range() is excluded.

   Answer

   (D)

   A is false: 5 is not produced. R is true and is the reason why.

5. Assertion (A): A logical error does not stop the execution of a program.

   Reason (R): Python detects logical errors before running the program.

   Answer

   (C)

   A is true: the program runs and gives a wrong result. R is false: Python cannot detect logical errors at all.

Short answer

1. 2 marks

   Differentiate between interactive mode and script mode of Python. (Any two points)

   Answer

   1. In interactive mode, statements are typed at the >>> prompt and executed one at a time; in script mode, a complete program is written in a file and run together.
   2. Interactive-mode code is not saved, whereas a script is saved with a .py extension and can be reused.
   3. Interactive mode shows the value of an expression automatically; script mode needs print().
2. 2 marks

   Identify the valid and invalid identifiers, giving a reason for each invalid one: Sales2026, net pay, _tax, import, 3rdRank, rate%

   Answer

   Valid: Sales2026, _tax.

   Invalid: net pay (contains a space), import (keyword), 3rdRank (starts with a digit), rate% (contains the special symbol %).

3. 2 marks

   What are mutable and immutable data types? Give two examples of each.

   Answer

   A mutable data type allows its value to be changed in place after creation, for example list and dict.

   An immutable data type does not allow its value to be changed in place; any change creates a new object. Examples: int, float, str, tuple.

4. 2 marks

   Evaluate the following expressions, showing the steps:

   (a) 30 - 4 * 3 ** 2 // 5

   (b) not 15 > 10 and 7 % 2 == 1

   Answer

   (a) 3 ** 2 = 9 → 4 * 9 = 36 → 36 // 5 = 7 → 30 - 7 = 23

   (b) 15 > 10 is True and 7 % 2 == 1 is True. not True = False; False and True = False

   print(30 - 4 * 3 ** 2 // 5)
   print(not 15 > 10 and 7 % 2 == 1)

   Output

   23
   False

5. 2 marks

   Predict the output of the following code.

   s = 0
   for i in range(1, 10, 2):
       s = s + i
       print(s, end=" ")
   print("|", s)

   Answer

   The loop runs for i = 1, 3, 5, 7, 9 and adds them to s. Inside the loop only the running total is printed on one line.

   s = 0
   for i in range(1, 10, 2):
       s = s + i
       print(s, end=" ")
   print("|", s)

   Output

   1 4 9 16 25 | 25

6. 2 marks

   Rewrite the following code after removing the errors. Underline each correction.

   num = Int(input("Enter a number: ")
   If num % 2 = 0
       print("Even")
   else
       Print("Odd")

   Answer

   Corrections: Int → int (case), add closing bracket on line 1, If → if, = → ==, colon after the condition, else needs a colon, and Print → print. The corrected code is:

   num = int(input("Enter a number: "))
   if num % 2 == 0:
       print("Even")
   else:
       print("Odd")

   Output

   Enter a number: 14
   Even

7. 2 marks

   Name the type of error in each case: (a) a closing quote is missing in a print() statement; (b) the program tries to use a variable that was never assigned; (c) area of a rectangle is calculated as 2 * (l + b); (d) int("twenty").

   Answer

   (a) Syntax error

   (b) Runtime error (NameError)

   (c) Logical error (that is the perimeter formula)

   (d) Runtime error (ValueError)

8. 2 marks

   What is the difference between = and ==? Give an example of each.

   Answer

   = is the assignment operator; it stores a value in a variable, e.g. marks = 90.

   == is a relational operator; it compares two values and returns True or False, e.g. marks == 90 gives True when marks is 90.

9. 2 marks

   Write the output of the following code.

   for r in range(1, 4):
       for c in range(r):
           print("*", end="")
       print()

   Answer

   The outer loop runs 3 times; for row r the inner loop prints * r times.

   for r in range(1, 4):
       for c in range(r):
           print("*", end="")
       print()

   Output

   *
   **
   ***

10. 2 marks

    What is type conversion? Differentiate between implicit and explicit conversion with an example each.

    Answer

    Changing a value from one data type to another is type conversion.

    Implicit: done automatically by Python, e.g. 5 + 2.5 gives 7.5 (int converted to float).

    Explicit: done by the programmer with a function, e.g. int("25") + 5 gives 30.

11. 2 marks

    Convert the following for loop into an equivalent while loop.

    for k in range(20, 4, -5):
        print(k)

    Answer

    The control variable is initialised before the loop, tested in the while line and decreased inside the body:

    k = 20
    while k > 4:
        print(k)
        k = k - 5

    Output

    20
    15
    10
    5

12. 2 marks

    What is the role of indentation in Python? What happens if a statement inside an if block is not indented?

    Answer

    Indentation (leading spaces) marks which statements belong to a block, such as the body of an if, else or a loop. All statements of a block must have the same indentation. If the statement after if ...: is not indented, Python raises an IndentationError and the program does not run.

Long answer

1. 3 marks

   Explain any three types of operators in Python with two examples each. (3 marks)

   Answer

   1. Arithmetic operators perform calculations: 17 // 5 gives 3, 2 ** 4 gives 16.
   2. Relational operators compare values and give True/False: 45 > 30 gives True, "abc" == "ABC" gives False.
   3. Logical operators combine conditions: marks >= 33 and attendance >= 75; not (age < 18).

   (Membership in/not in and identity is/is not may also be explained.)

2. 3 marks

   What is debugging? Explain the three types of errors with one example each. (3 marks)

   Answer

   Debugging is finding and removing errors from a program.

   1. Syntax error: breaks the rules of the language; the program does not run. Example: while x < 5 (colon missing).
   2. Runtime error: occurs during execution and stops the program abruptly. Example: print(100 / 0) gives ZeroDivisionError.
   3. Logical error: the program runs but gives a wrong output because of wrong logic. Example: avg = a + b / 2 instead of (a + b) / 2.
3. 3 marks

   Write a program to input the cost price and selling price of an item and print whether there is a profit or a loss, and of how much. Also print the profit or loss percentage. (3 marks)

   Answer

   Program with a sample run:

   cp = float(input("Enter cost price: "))
   sp = float(input("Enter selling price: "))
   if sp > cp:
       profit = sp - cp
       print("Profit of Rs", profit)
       print("Profit % =", round(profit / cp * 100, 2))
   elif cp > sp:
       loss = cp - sp
       print("Loss of Rs", loss)
       print("Loss % =", round(loss / cp * 100, 2))
   else:
       print("No profit, no loss")

   Output

   Enter cost price: 1250
   Enter selling price: 1400
   Profit of Rs 150.0
   Profit % = 12.0

4. 3 marks

   Write a program that reads a number and prints its multiplication table up to 10 in the format 7 x 1 = 7. Also print the sum of all the multiples. (3 marks)

   Answer

   Program with a sample run:

   n = int(input("Enter a number: "))
   total = 0
   for i in range(1, 11):
       print(n, "x", i, "=", n * i)
       total += n * i
   print("Sum of multiples:", total)

   Output

   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
   Sum of multiples: 385

5. 5 marks

   Write a program to input a positive integer and print: (a) the number of digits, (b) the sum of the digits, (c) whether it is a palindrome. Use a while loop. (5 marks)

   Answer

   A copy of the number is kept so that it can be compared with the reverse at the end.

   n = int(input("Enter a positive integer: "))
   temp = n
   digits = 0
   s = 0
   rev = 0
   while temp > 0:
       d = temp % 10
       digits += 1
       s += d
       rev = rev * 10 + d
       temp //= 10
   print("Number of digits:", digits)
   print("Sum of digits:", s)
   if rev == n:
       print(n, "is a palindrome")
   else:
       print(n, "is not a palindrome")

   Output

   Enter a positive integer: 12321
   Number of digits: 5
   Sum of digits: 9
   12321 is a palindrome

6. 5 marks

   An electricity board charges as follows: first 100 units at Rs 4 per unit, next 100 units at Rs 6 per unit, and units above 200 at Rs 8 per unit. A fixed charge of Rs 50 is added to every bill. Write a program to input units consumed and print the bill. (5 marks)

   Answer

   The slabs are handled with an if-elif-else ladder; each slab charges only the units that fall inside it.

   units = int(input("Enter units consumed: "))
   if units <= 100:
       charge = units * 4
   elif units <= 200:
       charge = 100 * 4 + (units - 100) * 6
   else:
       charge = 100 * 4 + 100 * 6 + (units - 200) * 8
   bill = charge + 50
   print("Energy charge: Rs", charge)
   print("Total bill: Rs", bill)

   Output

   Enter units consumed: 265
   Energy charge: Rs 1520
   Total bill: Rs 1570

7. 3 marks

   Explain the for loop and the range() function with its three forms. Write the output of for i in range(15, 2, -4): print(i, end=" "). (3 marks)

   Answer

   A for loop repeats its body once for each item of a sequence. range() creates a sequence of integers: range(stop) from 0 to stop-1; range(start, stop) from start to stop-1; range(start, stop, step) in jumps of step (negative step counts down). The stop value is never included.

   For the given loop the values are 15, 11, 7, 3:

   for i in range(15, 2, -4): print(i, end=" ")

   Output

   15 11 7 3

8. 3 marks

   Write a program to print the following pattern for n rows (n is input by the user). Sample for n = 4:

   1

   2 2

   3 3 3

   4 4 4 4

   (3 marks)

   Answer

   Row i prints the number i, i times, using a nested loop:

   n = int(input("Enter number of rows: "))
   for i in range(1, n + 1):
       for j in range(i):
           print(i, end=" ")
       print()

   Output

   Enter number of rows: 4
   1 
   2 2 
   3 3 3 
   4 4 4 4

Case-based

price = input("Enter price: ")
qty = int(input("Enter quantity: "))
amount = price * qty
gst = amount * 5 / 100
print("Total:", amount + gst)

Enter price: 40
Enter quantity: 3
TypeError: unsupported operand type(s) for /: 'str' and 'int'

>>> a = 17
>>> b = 5
>>> a // b
3
>>> a % b
2
>>> a / b
3.4
>>> a ** 2 > 250 and b != 5
False

Practicals

total = 0
for i in range(1, 6):
    m = float(input("Enter marks in subject " + str(i) + ": "))
    total += m
avg = total / 5
if avg >= 90:
    grade = "A1"
elif avg >= 75:
    grade = "A2"
elif avg >= 60:
    grade = "B"
elif avg >= 33:
    grade = "C"
else:
    grade = "Fail"
print("Total =", total)
print("Average =", avg)
print("Grade =", grade)

Enter marks in subject 1: 82
Enter marks in subject 2: 76
Enter marks in subject 3: 91
Enter marks in subject 4: 68
Enter marks in subject 5: 88
Total = 405.0
Average = 81.0
Grade = A2

price = float(input("Enter marked price: "))
if price <= 2000:
    rate = 5
elif price <= 5000:
    rate = 10
else:
    rate = 15
discount = price * rate / 100
sale_price = price - discount
print("Discount @", rate, "% = Rs", discount)
print("Sale price = Rs", sale_price)

Enter marked price: 3600
Discount @ 10 % = Rs 360.0
Sale price = Rs 3240.0

p = float(input("Enter principal: "))
r = float(input("Enter rate of interest (% per year): "))
t = float(input("Enter time (years): "))
si = p * r * t / 100
amount = p * (1 + r / 100) ** t
ci = amount - p
print("Simple Interest = Rs", round(si, 2))
print("Compound Interest = Rs", round(ci, 2))

Enter principal: 50000
Enter rate of interest (% per year): 8
Enter time (years): 3
Simple Interest = Rs 12000.0
Compound Interest = Rs 12985.6

p = float(input("Enter loan amount: "))
annual_rate = float(input("Enter annual interest rate (%): "))
years = int(input("Enter period in years: "))
r = annual_rate / 12 / 100
n = years * 12
emi = p * r * (1 + r) ** n / ((1 + r) ** n - 1)
total = emi * n
print("Monthly EMI = Rs", round(emi, 2))
print("Total payable = Rs", round(total, 2))
print("Total interest = Rs", round(total - p, 2))

Enter loan amount: 500000
Enter annual interest rate (%): 9
Enter period in years: 5
Monthly EMI = Rs 10379.18
Total payable = Rs 622750.66
Total interest = Rs 122750.66

item = input("Enter item name: ")
price = float(input("Enter price: "))
rate = int(input("Enter GST rate (5/12/18/28): "))
if rate in (5, 12, 18, 28):
    gst = price * rate / 100
    print("Item  :", item)
    print("Price : Rs", price)
    print("CGST @", rate / 2, "% : Rs", gst / 2)
    print("SGST @", rate / 2, "% : Rs", gst / 2)
    print("Total : Rs", price + gst)
else:
    print("Invalid GST rate")

Enter item name: School bag
Enter price: 1200
Enter GST rate (5/12/18/28): 18
Item  : School bag
Price : Rs 1200.0
CGST @ 9.0 % : Rs 108.0
SGST @ 9.0 % : Rs 108.0
Total : Rs 1416.0

import math
print("1. Rectangle  2. Square  3. Circle  4. Triangle")
ch = int(input("Enter your choice: "))
if ch == 1:
    l = float(input("Length: "))
    b = float(input("Breadth: "))
    print("Area =", l * b, " Perimeter =", 2 * (l + b))
elif ch == 2:
    s = float(input("Side: "))
    print("Area =", s * s, " Perimeter =", 4 * s)
elif ch == 3:
    r = float(input("Radius: "))
    print("Area =", round(math.pi * r * r, 2), " Circumference =", round(2 * math.pi * r, 2))
elif ch == 4:
    a = float(input("Side a: "))
    b = float(input("Side b: "))
    c = float(input("Side c: "))
    s = (a + b + c) / 2
    area = math.sqrt(s * (s - a) * (s - b) * (s - c))
    print("Area =", round(area, 2), " Perimeter =", a + b + c)
else:
    print("Invalid choice")

1. Rectangle  2. Square  3. Circle  4. Triangle
Enter your choice: 4
Side a: 5
Side b: 6
Side c: 7
Area = 14.7  Perimeter = 18.0

text = input("Enter a sentence: ")
vowels = consonants = others = 0
for ch in text:
    if ch in "aeiouAEIOU":
        vowels += 1
    elif ("a" <= ch <= "z") or ("A" <= ch <= "Z"):
        consonants += 1
    else:
        others += 1
print("Vowels:", vowels)
print("Consonants:", consonants)
print("Other characters:", others)

Enter a sentence: Incredible India 2026!
Vowels: 7
Consonants: 8
Other characters: 7

total = 0
for i in range(1, 101):
    total += i ** 2
print("Sum of squares of first 100 natural numbers =", total)

n = int(input("Enter the number: "))
k = int(input("How many multiples? "))
for i in range(1, k + 1):
    print(n * i, end=" ")
print()

Sum of squares of first 100 natural numbers = 338350
Enter the number: 12
How many multiples? 8
12 24 36 48 60 72 84 96

Common mistakes

• Using a value from input() as a number without converting it. input() always returns a string, so write marks = int(input("Marks: ")).

• Writing = in a condition instead of ==, as in if marks = 100:. = assigns a value; == compares two values.

• Forgetting the colon at the end of if, elif, else, for and while lines, which gives a SyntaxError.

• Mixing tabs and spaces or indenting statements of one block unequally, which gives an IndentationError. Use 4 spaces consistently.

• Expecting range(1, 10) to include 10. The stop value is always excluded; use range(1, 11) for 1 to 10.

• Thinking / gives an integer. 10 / 2 is 5.0; use // when a whole-number quotient is required.

• Writing Print, If or True as true. Python is case-sensitive; keywords and built-in names must be typed exactly.

• Forgetting to update the control variable inside a while loop, which creates an infinite loop.