Python mid sem

SECTION A - Quick Concepts (1 mark each)

Set 1 Questions

Q1. Which function displays output on the screen?

Answer: print()
Logic: Think "print" = show on screen, like printing on paper

Q2. Syntax to declare a list with 10, 20, 30?

Answer: numbers = [10, 20, 30]
Logic: Lists use square brackets [] - think of it as a "box" holding items

Q3. Difference between == and is?

Answer:

• == checks if VALUES are same (like comparing what's written on two papers)

• is checks if it's the SAME OBJECT in memory (like checking if two papers are actually the same physical paper)

Example:

a = [1,2,3]
b = [1,2,3]
a == b  # True (same content)
a is b  # False (different objects in memory)

Q4. Keyword to define a function?

Answer: def
Logic: "def" = "define" a function

Q5. Output of print(type({1,2,3}))?

Answer: <class 'set'>
Logic: Curly braces {} with comma-separated values = set (unique items, no duplicates)

Q6. Difference between mutable and immutable?

Answer:

• Mutable = Can change (list, dict, set) - think "mutable" = "modifiable"

• Immutable = Cannot change (tuple, str, int, float) - think "immutable" = "permanent"

Q7. Error in if x=5: print('Hello')?

Answer: Use == not =
Logic:

• = is for assignment (giving a value)

• == is for comparison (checking if equal)

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Set 2 Questions

Q1. Function to find string length?

Answer: len()
Logic: "len" = "length"

Q2. Syntax to create dictionary with name and age?

Answer: student = {"name": "Alice", "age": 20}
Logic: Dictionary uses curly braces with key: value pairs

Q3. Difference between break and continue?

Answer:

• break = Exit the entire loop (break out completely)

• continue = Skip current iteration, continue with next (skip one, keep going)

Q4. Module for mathematical operations?

Answer: math
Logic: Import with import math, then use math.sqrt(), math.sin(), etc.

Q5. Output of x = "123" then print(x*2)?

Answer: 123123
Logic: String multiplication repeats the string

Q6. Difference between local and global variables?

Answer:

• Local = Inside function only (dies when function ends)

• Global = Outside function, accessible everywhere (lives throughout program)

Q7. Error in for i in range(5) print(i)?

Answer: Missing colon :
Logic: All control structures (if, for, while) need colon at end

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📖 SECTION B - Detailed Problems (5 marks each)

Set 1 - Q8: Lists vs Tuples

Key Differences:

Logic:

• Lists = Shopping list (can add/remove items)

• Tuples = Birth date (never changes)

Example:

my_list = [1,2,3]
my_list[0] = 10  # Works! ✓

my_tuple = (1,2,3)
my_tuple[0] = 10  # Error! ✗

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Set 1 - Q9: Prime Number Checker

Logic (Step by step):

1. Prime must be > 1

2. Only divisible by 1 and itself

3. Check divisors from 2 to √n (optimization: no need to check beyond square root)

Program:

num = int(input("Enter number: "))

if num > 1:
    for i in range(2, int(num**0.5) + 1):
        if num % i == 0:
            print('Not prime')
            break
    else:  # else runs if loop completes without break
        print('Prime')
else:
    print('Not prime')

Why √n? If n = 36, factors are: 1×36, 2×18, 3×12, 4×9, 6×6. After 6, it's just reversed pairs!

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Set 1 - Q10: Fibonacci Function

Logic: Each number = sum of previous two (0, 1, 1, 2, 3, 5, 8...)

Program:

def fibonacci(n):
    fib = [0, 1]  # Start with first two
    while len(fib) < n:
        fib.append(fib[-1] + fib[-2])  # Add last two
    return fib[:n]  # Return first n numbers

print(fibonacci(7))
# Output: [0, 1, 1, 2, 3, 5, 8]

Memory Trick: Fibonacci = "Fee-bo-nah-chee" sounds like counting in a fancy way!

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Set 1 - Q11: BankAccount Class

Logic: Class = Blueprint for objects (like a form), Object = Filled form

Program:

class BankAccount:
    def __init__(self, balance=0):
        self.balance = balance  # Constructor sets initial state

    def deposit(self, amt):
        self.balance += amt
        print('Deposited:', amt)

    def withdraw(self, amt):
        if amt <= self.balance:
            self.balance -= amt
            print('Withdrawn:', amt)
        else:
            print('Insufficient balance')

    def display(self):
        print('Balance:', self.balance)

# Driver code
acc = BankAccount(1000)
acc.deposit(500)   # Balance: 1500
acc.withdraw(200)  # Balance: 1300
acc.display()      # Shows: 1300

Key Concept: self = "this specific account" (not all accounts)

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Set 1 - Q12: Word Frequency Counter

Logic: Dictionary stores word as key, count as value

Program:

word_count = {}

with open('sample.txt') as f:
    for line in f:
        for word in line.split():
            word = word.lower().strip('.,!?')  # Clean word
            word_count[word] = word_count.get(word, 0) + 1

print(word_count)

How it works:

• .get(word, 0) returns count if exists, else 0

• Add 1 each time word appears

• Result: {'hello': 3, 'world': 2, ...}

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Set 1 - Q13: Second Largest Number

Logic: Track two variables: first (largest) and second (second largest)

Program:

numbers = [12, 45, 7, 34, 45, 23]
first = second = float('-inf')  # Start with smallest possible

for num in numbers:
    if num > first:
        second = first  # Old first becomes second
        first = num     # New first
    elif num > second and num != first:
        second = num    # Update second only

print('Second Largest:', second)
# Output: 34

Visual:

[12, 45, 7, 34, 45, 23]
 ↓   ↓      ↓
12→ 45(skip, duplicate)→ 34(second!)

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Set 2 - Q8: For vs While Loops

Key Difference:

• for = Know how many times (count-based)

• while = Don't know, depends on condition (condition-based)

Examples:

# FOR: Print 0 to 4 (know it's 5 times)
for i in range(5):
    print(i)

# WHILE: Print until user says "stop"
while input("Continue? ") != "stop":
    print("Running...")

Memory: FOR = "FORward with fixed steps", WHILE = "WHILE condition is true"

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Set 2 - Q9: Palindrome Checker

Logic: Word reads same forwards and backwards (like "mom", "racecar")

Program:

s = input('Enter a string: ')

if s == s[::-1]:  # Reverse with slicing
    print('Palindrome')
else:
    print('Not Palindrome')

Slicing Trick: [::-1] means start:end:step, where step=-1 reverses

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Set 2 - Q10: Factorial Using Recursion

Logic: n! = n × (n-1)!
Example: 5! = 5 × 4 × 3 × 2 × 1 = 120

Program:

def factorial(n):
    if n == 0 or n == 1:  # Base case
        return 1
    else:
        return n * factorial(n-1)  # Recursive call

print(factorial(5))
# Output: 120

How it works:

factorial(5)
= 5 × factorial(4)
= 5 × 4 × factorial(3)
= 5 × 4 × 3 × factorial(2)
= 5 × 4 × 3 × 2 × factorial(1)
= 5 × 4 × 3 × 2 × 1
= 120

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Set 2 - Q11: Student Class with Average

Logic: Class stores student data, method calculates average

Program:

class Student:
    def __init__(self, name, marks):
        self.name = name
        self.marks = marks  # List of marks

    def average(self):
        return sum(self.marks) / len(self.marks)

s1 = Student('Rahul', [85, 90, 95])
print('Name:', s1.name)
print('Average:', s1.average())
# Output: Name: Rahul, Average: 90.0

Key: sum() adds all, len() counts items

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Set 2 - Q12: Sum Numbers from File

Logic: Read file line by line, convert to int, add to total

Program:

total = 0

with open('numbers.txt', 'r') as f:
    for line in f:
        total += int(line.strip())  # strip() removes \n

print('Sum:', total)

Why with? Automatically closes file (good practice!)

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Set 2 - Q13: Remove Duplicates Without set()

Logic: Check if item already in new list before adding

Program:

numbers = [1, 2, 3, 2, 4, 3, 5, 1, 6]
unique = []

for num in numbers:
    if num not in unique:  # Not seen before?
        unique.append(num)  # Add it!

print('Without duplicates:', unique)
# Output: [1, 2, 3, 4, 5, 6]

Alternative (using set): unique = list(set(numbers)) (but question says don't use set!)

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Quick Revision Tips

Mutable vs Immutable (Most Asked!)

• Mutable (Can Change): list, dict, set

• Immutable (Cannot Change): tuple, str, int, float, bool

File Handling Pattern

with open('file.txt', 'r') as f:  # 'r'=read, 'w'=write
    content = f.read()

Class Structure

class ClassName:
    def __init__(self, params):  # Constructor
        self.attribute = params

    def method(self):  # Method
        return something

Common Errors to Avoid

1. Forgetting colon : after if/for/while/def

2. Using = instead of == for comparison

3. Indentation errors (Python is strict!)

4. Forgetting self in class methods

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Last-Minute Checklist

• [ ] print() for output, input() for input

• [ ] Lists use [], tuples use (), sets use {}, dicts use {key: value}

• [ ] == checks value, is checks identity

• [ ] break exits loop, continue skips iteration

• [ ] Files opened with with auto-close

• [ ] self refers to current object in classes

• [ ] Recursion needs base case to stop

• [ ] [::-1] reverses strings/lists

Good luck with your exam! 🚀