It should be person["bmi"] = person["weight"] / person["height"] ** 2 More on reddit.com

Thoughts: Codewars Advent of Code r/dailyprogrammer (not updated "daily" anymore, but go through the history) More on reddit.com

Here are some often recommended resources: Exercism , Hackinscience and Practicepython — these are all beginner friendly and difficulty levels are marked Adventofcode , Codewars , Python Morsels — includes more challenging exercises for intermediate to advanced level users Checkio , Codingame , Codecombat — gaming based challenges /r/dailyprogrammer — not active currently, but there's plenty of past challenges with discussions And here are some resources for projects: Projects with solutions — algorithms, data structures, networking, security, databases, etc Project based learning — web applications, bots, data science, machine learning, etc Books: The Big Book of Small Python Projects Tiny Python Projects /r/learnpython: What do you automate with Python at home? More on reddit.com

Let me walk you through the code: name = 'World' Somewhere in memory, Python creates a new string object with the characters W, o, r, l, d. A variable is created with the name name and is assigned to reference the new string object. line = '-' Somewhere in memory, Python creates a new string object with the character -. A variable is created with the name line and is assigned to reference the new string object. for char in name: A loop is created which iterates over the string object referenced by name. On each iteration, a new string object is created to hold the single character from the current iteration, and char is assigned the memory location of that single character object. line = line + char The expression on the right is evaluated first. The two string objects referenced by the two variables are retrieved and concatenated (which is what the __add__ method for the str class does for the + operator). This creates a new string object somewhere in memory. The variable line is re-assigned to reference the new string object. The string object it referenced before this now has nothing referencing it and so Python can reclaim the memory occupied by that older object (deleting the object). Strings are immutable, so a string object cannot be changed. You have to create new string objects. You should no be able to see that the character "-" is not going to appear between each letter because it exists alone only on the first assignment to line. print(line) Python passes the reference held by line to the print function which uses the default representation for output whatever latest iteration of the string object line references at that point. More on reddit.com