Discover challenging Python brain teasers that test your skills and stretch your thinking. Gain insights into advanced concepts and enhance your understanding of this versatile language.

Forget Scrabble, Boggle, or Wordle. Tease your mind and test your skills with these fun brain teasers designed to stretch your thinking and expand your understanding of one of the most widely used languages out there. 

Python is simple. These puzzles are not. Good luck!

Python Brain Teasers

# Try it yourself
Try executing the code below to verify the results:

def add_n(items, n): 
  items += range(n)

items = [1] 
add_n(items, 3) 
print(items)

In [Puzzle 16: Call Me Maybe](https://www.educative.io/courses/python-brain-teasers/puzzle-16-explanation), we talked about rebinding versus mutation. Most of the time, `items += range(n)` is translated to `items = items + range(n)`, a process which is called **rebinding**.

In some cases, there is a special optimization for `+=`. Here’s a more detailed explanation from the Python documentation:

> An augmented assignment expression like `x += 1` can be rewritten as `x = x + 1` to achieve a similar, but not exactly equal, effect. In the augmented version, `x` is only evaluated once. Also, when possible, the actual operation is performed in-place, meaning that rather than creating a new object and assigning that to the target, the old object is modified instead.

A type defines how the `+` operator behaves with the `__add__` special method. It can also define `__iadd__` as a special case for `+=`. The book Learn Python in a Weekend below has more to say about how this works:

> These methods are called to implement the augmented arithmetic assignments (+=, -=, =, @=, /=, //=, %=, *=, <⇐, >>=, &=, ^=, |=). These methods should attempt to do the operation in place (modifying self) and return the result (which could be, but does not have to be, self). If a specific method is not defined, the augmented assignment falls back to the normal methods.


The built-in `list` object defines `__iadd__`, which calls the extend method.

What will happen if we change the code inside `add_n` to `items = items + range(n)`? 
We’ll get the exception below.

> `TypeError: can only concatenate list (not “range”) to list`

In Python 3, the built-in `range` function returns a range object. Even though it looks like it belongs in a list (`len`, `[]`, and `friends will work`), we can’t add it to a list.

If we want the rebinding code to work, we’ll need to write `items = items + list(range(n))`. Only then will the output be `[1]`.


As a general rule, try not to mutate the object passed to your functions. That style of programming is called **functional programming**. Functional code is easier to test and reason about. Give it a try. It’s fun!

Let’s find out how augmented arithmetic assignments work in Python.

Before We Begin

Python Puzzles

Wrapping Up

Puzzle 27: Explanation

Try it yourself