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Python Lists

Lists are used to store multiple items in a single variable. They are ordered, mutable (changeable), and allow duplicate values.

# Creating a list
fruits = ["apple", "banana", "cherry"]

# Mutating a list
fruits.append("orange")   # Adds to the end
fruits[1] = "mango"       # Modifies index 1
fruits.pop(0)             # Removes item at index 0

print(fruits)             # Output: ['mango', 'cherry', 'orange']

Python Tuples

Tuples are identical to lists, but with one critical difference: they are immutable (unchangeable). Once a tuple is created, you cannot change its values.

# Creating a tuple
coordinates = (10.5, 20.8)

# Tuples can be accessed like lists
print(coordinates[0])   # Output: 10.5

# ERROR: coordinates[0] = 11.5 
# "tuple object does not support item assignment"

Python Dictionaries

Dictionaries are used to store data values in key:value pairs. They are ordered (as of Python 3.7), changeable, and do NOT allow duplicate keys.

# Creating a dictionary
car = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}

# Accessing attributes via keys
print(car["brand"])     # Output: Ford
car["year"] = 2020      # Updates value

• Keys: Must be immutable types (String, Number, Tuple) and unique.
• Values: Can be of any data type (Lists, objects, even other Dicts).
• Using .get('key') is safer than [] because it avoids KeyErrors if missing.

Frequency of Values from 0-3

Task: Scan n values in the range 0-3 and print the number of times each value has occurred.

n = int(input("Enter number of values to read: "))
values = []

for i in range(n):
    val = int(input("Enter a value (0-3): "))
    if 0 <= val <= 3:
        values.append(val)
    else:
        print("Ignored: Value must be between 0 and 3.")

# Check count for 0, 1, 2, 3
for x in range(4):
    freq = values.count(x)
    print(f"Value {x} occurred {freq} times")

Tuple Average Calculation

Task: Create a tuple to store n numeric values and find the average of all values.

n = int(input("Enter number of values: "))
temp_list = []

# Lists are easier to build dynamically than Tuples
for i in range(n):
    num = float(input("Enter numeric value: "))
    temp_list.append(num)

# Convert list to tuple
num_tuple = tuple(temp_list)

if len(num_tuple) > 0:
    avg = sum(num_tuple) / len(num_tuple)
    print(f"Tuple: {num_tuple}")
    print(f"Average: {avg:.2f}")

The Runner-Up Score

Task: Input a list of scores for N students. Find the score of the runner-up.

n = int(input("N = "))
input_string = input("Scores= ")

# The split() splits the string by spaces.
# List comprehension converts strings to integers.
scores = [int(x) for x in input_string.split()]

# Remove duplicates to handle multiple maximum scores
unique_scores = list(set(scores))

# Sort in descending order
unique_scores.sort(reverse=True)

# The 0th index is highest, 1st index is runner-up
print(unique_scores[1])

Students & Cities Dictionary

Task: Create a dictionary linking Names (keys) to Cities (values) and execute multiple queries.

persons = {"Alice": "Paris", "Bob": "London", "Charlie": "Paris"}

# a) Display all names (Keys)
print("Names:", list(persons.keys()))

# b) Display all cities (Values)
print("Cities:", list(persons.values()))

# c) Display student name and city
for name, city in persons.items():
    print(f"{name} -> {city}")

# d) Count number of students in each city
city_count = {}
for city in persons.values():
    # .get(city, 0) handles cases where city key is not made yet
    city_count[city] = city_count.get(city, 0) + 1

print("Counts:", city_count)

Nested Movie Dictionary

Task: Create a dictionary holding another dictionary (Name -> {Year, Director, Cost, Earnings}). Query specific movies.

movies = {
    "Inception": {"year":2010, "dir":"Nolan", "cost":160, "earn":836},
    "Avatar":    {"year":2009, "dir":"Cameron","cost":237, "earn":2900},
    "Dune":      {"year":2021, "dir":"Villeneuve","cost":165, "earn":400}
}
print("--- Movies Before 2015 ---")
for name, info in movies.items():
    if info["year"] < 2015:  print(name)

print("--- Movies Making Profit ---")
for name, info in movies.items():
    if info["earn"] > info["cost"]: print(name)

print("--- Movies by Nolan ---")
for name, info in movies.items():
    if info["dir"] == "Nolan": print(name)

Contact Book Manager

Task: Create a persistent CRUD (Create, Read, Update, Delete) program using a Dictionary.

contacts = {}
while True:
    ch = int(input("1.Add 2.Search 3.Delete 4.Exit : "))
    
    if ch == 1:
        name = input("Name: ")
        contacts[name] = input("Phone: ")
        
    elif ch == 2:
        name = input("Name to search: ")
        print("Found:", contacts.get(name, "Not Found"))
        
    elif ch == 3:
        name = input("Name to delete: ")
        if name in contacts:
            del contacts[name]
            print("Deleted.")
            
    elif ch == 4: break

Todo List Manager

Task: Create an infinite loop permitting users to push and pop tasks out of a List array.

todos = []
while True:
    print("1.Add Task  2.View Tasks  3.Remove Task  4.Exit")
    ch = int(input("Choice: "))
    
    if ch == 1:
        todos.append(input("Enter new task: "))
        
    elif ch == 2:
        for idx, task in enumerate(todos):
            print(f"Task {idx+1}: {task}")
            
    elif ch == 3:
        idx = int(input("Enter Task Number to Remove: ")) - 1
        if 0 <= idx < len(todos):
            removed = todos.pop(idx)
            print(f"{removed} successfully removed.")
        else:
            print("Invalid ID.")
            
    elif ch == 4: break