Practice Problems

Write a Python program that prints the exact message: Hello, Python learner!

Simple Calculator

Write a function add(a, b) that returns the sum of two numbers.

Sum of Three Numbers

Write a function sum_of_three(a, b, c) that returns the sum of three numbers. This reinforces defining and calling functions with multiple parameters.

Greet the User

Write a program that asks the user for their name using input() and then prints a greeting in the format: Hello, <name>!

Sum of Two String Numbers

Write a function sum_two_strings(a, b) where a and b are strings representing integers. Convert them to integers and return their numeric sum.

Loops(2 problems)

Average Student Marks

Given a list of integer marks, write a function average_mark(marks) that returns the average as a float.

Count Passing Students

Given a list of integer marks, write a function count_pass(marks) that returns how many marks are 40 or above.

Conditionals(1 problem)

Classify Exam Grade

Write a function grade(score) that returns 'A', 'B', 'C', or 'D' based on the numeric score using if/elif/else.

Strings(4 problems)

Count Vowels in a String

Write a function count_vowels(text) that returns how many vowels (a, e, i, o, u) appear in the string, ignoring case.

Reverse a String

Write a function reverse_string(text) that returns the input string in reverse order.

Format a Sentence

Write a function format_msg(name, score) that returns a string formatted as: 'User {name} scored {score} points.'

Extract Email Domain

Write a function get_domain(email) that returns the domain part of an email address (everything after the '@' symbol).

Arrays Lists(3 problems)

Access First and Last

Write a function get_ends(items) that returns a new list containing only the first and last elements of the input list.

Growing the List

Write a function manage_list(items) that adds 'apple' to the end and 'milk' at index 1, then returns the modified list.

Shrinking the List

Write a function shrink_list(items) that removes 'banana' from the list and pops the last element, then returns the list.

List Operations(5 problems)

Extract the Middle

Given a list of 4 items, write a function get_middle(items) that returns the middle two elements using slicing.

Reverse without Methods

Write a function manual_reverse(items) that returns a reversed copy of the list WITHOUT using the .reverse() method or slicing.

Find Min and Max

Write a function get_extremes(items) that returns a tuple (min_val, max_val) containing the smallest and largest numbers in the list.

To-Do List Manager

Write a function manage_todo(tasks, done_index) that removes the task at done_index and returns the remaining tasks as a formatted string: 'Remaining: task1, task2...'

Filter Even Numbers

Write a function filter_even(numbers) that returns a new list containing only the even numbers from the input list.

Comprehensions(2 problems)

Flatten a Grid

Write a function flatten(grid) that takes a 2D list (list of lists) and returns a single 'flattened' list of all elements.

Squares with Comprehension

Write a function squares(n) that returns a list of squares from 0 to n-1 using a list comprehension.

Dictionaries(1 problem)

Word Frequency Counter

Write a function word_frequency(words) that takes a list of strings and returns a dictionary mapping each word to how many times it appears.

Sets(1 problem)

Unique Items from a List

Write a function unique_items(items) that returns a set containing all unique items from the input list.

Exceptions(1 problem)

Safe Division

Write a function safe_divide(a, b) that returns a / b, but if b is zero, returns the string 'Cannot divide by zero'. Use try/except.

Files(2 problems)

Count Lines in a File

Write a function count_lines(path) that opens a text file and returns how many lines it contains.

Write to a File

Write a function write_message(filename, message) that writes the given message to a file with the given filename. (Note: In this web environment, valid file I/O is simulated.)

2 hints available

Classes(2 problems)

Create a Person Class

Create a Person class with 'name' and 'age' attributes. Add a method 'introduce()' that returns the string: 'Hi, my name is [name]'.

2 hints available

Student Class & Logic

Define a Student class with name and marks attributes and an is_pass method that returns True if marks are 40 or above.

Functions(1 problem)

Password Strength Analyzer

Create a function `analyze_password(password)` that returns True if a password is 'strong' (length >= 8 and contains a digit), and False otherwise. Bonus: Use a default argument `min_length=8`.

Advanced Structures(1 problem)

You are managing a game inventory. Write a function `update_inventory(current_inv, new_items)` that takes a list of current items and a list of new items, and returns a `Counter` object of the total inventory.

Iterators(1 problem)

Log File Processor

Write a generator function `process_logs(logs)` that takes a list of log strings (e.g., 'ERROR: Disk full') and yields only the messages that start with 'ERROR:'.

Functional(1 problem)

Data Cleaning Pipeline

Write a function `clean_data(scores)` that takes a list of numbers. It relies on a pipeline: 1. Filter out invalid scores (must be >= 0). 2. Cap any score > 100 to 100. 3. Return the sum of the cleaned scores. Use `filter`, `map`, and `sum` (or `reduce`).

Modules(1 problem)

Safe Math Importer

Write a function `safe_sqrt(n)` that imports the `math` module inside the function and returns the square root of `n`. If `n` is negative, return -1. (Note: In production, imports usually go at the top, but this exercises local scope imports).

Advanced Oop(1 problem)

Bank Account Property

Create a class `BankAccount` with a private attribute `_balance`. Add a `@property` called `balance` to get it. Add a `@balance.setter` that raises a `ValueError` if the new balance is negative.

External Data(1 problem)

JSON Data Extractor

Write a function `extract_emails(json_str)` that takes a JSON string containing a list of users, and returns a list of their email addresses. If the JSON is invalid, return an empty list.

Testing(1 problem)

Mini Unit Tester

Write a function `run_test(func, input_val, expected)` that calls `func(input_val)`. If the result equals `expected`, return 'PASS'. If not, return 'FAIL: Expected {expected}, got {actual}'.

Pythonic(1 problem)

Refactor to One-Liner

Refactor the following logic into a single list comprehension: Create a list of squared even numbers from the input list `numbers`.

Problem Solving(1 problem)

Algorithm Designer

Implement a function `find_peak(nums)` that finds a peak element in a list of integers. A peak is an element strictly greater than its neighbors. For corner elements, we assume the neighbor out of bounds is minus infinity. Return the index of any peak.

Future Tech(1 problem)

Tiny Neural Neuron

Simulate a single neuron's forward pass. Write `neuron(inputs, weights, bias)` that calculates the dot product of inputs and weights, adds bias, and applies a ReLU activation (return x if x > 0 else 0).

Essential Algorithms(5 problems)

Binary Search Implementation

Write a function `binary_search(arr, target)` that returns the index of the target in a sorted list, or -1 if not found. Use the efficient O(log n) approach.

Divide and Conquer: Quick Sort

Implement the Quick Sort algorithm. Given a list of numbers, return a new sorted list using the recursive divide-and-conquer approach.

Social Network BFS

Find the shortest path distance (number of edges) between two nodes in an adjacency list graph using BFS. Return -1 if no path exists.

The Knapsack Problem

Write a function `knapsack(weights, values, capacity)` that returns the maximum value that can fit into the given capacity using 0/1 logic (use DP).

Huffman Tree Frequencies

Implement the frequency map part of Huffman Compression. Given a string, return a dictionary mapping each character to its frequency count.