Gain insights into Python 3 by learning basic concepts like keywords and data types, and delving into 50 code puzzles that enhance your understanding of classes and functions.

This course acts as a stepping stone to becoming a Python master. Before getting into advanced concepts like classes and functions, the course begins with Python's basic concepts, such as keywords and data types. Later in this course, you'll be going through 50 code puzzles that will teach you different concepts in Python 3.

An Intro to Python 3

# Puzzle 42

**Which of the following functions correctly sorts the list?**

> **Note**: Enter the output you guessed. Then, press the **Run** button, and your new Elo will be calculated. Don't forget to save your Elo rating.

#############################
## id 195
## Puzzle Elo 1672
## Correctly solved 67 %
#############################

def qsort1(L):
  if L:
    return qsort1([x for x in L[1:] 
                  if x < L[0]]) + L[:1] \
                     + qsort1([x for x in L[1:] if x  >= L[0]])
  return []

def qsort2(L):
  if L:
    return L[:1] + qsort2([x for x in L[1:] 
      if x < L[0]]) \
         + qsort2([x for x in L[1:] if x  >= L[0]])
         
  return []


print(qsort1([0, 33, 22]))
print(qsort2([0, 33, 22]))


## Quicksort

This puzzle introduces a recursive algorithm to sort lists. When executing the functions, you get the following results:

  `print(qsort1([0,33,22]))` -> output:  `[0,22, 33]`

   `print(qsort2([0,33,22]))` -> output:  `[0, 33, 22]`

So based on this output, the function `qsort1` correctly sorts the list. But why? 

The algorithm is a variant of the popular quicksort algorithm. Quicksort selects a `pivot` element from the list. In the puzzle, it selects the first element of the list, i.e., `L[0]`. Then, the algorithm moves all elements that are smaller than the `pivot` to the left side. Similarly, it moves elements that are larger than or equal to the `pivot` to the right side.
This is repeated recursively for the left and the right lists.

Suppose you create a new list as follows. You put all elements that are smaller than the `pivot` on the left, then the `pivot`, and then all elements that are larger than or equal to the `pivot` on the right. The resulting list feels a bit more sorted, right? If the two sublists were already sorted, the list would be perfectly sorted. This is where the recursive call of `qsort1` comes into play. It takes over the problem of sorting each sublist by applying the same scheme of pivoting and recursion to the sublist.

In contrast, the `qsort2` function appends both sublists to the right of the pivot element. Hence, the list is already unsorted after the first recursion level.

## Solution

The correct solution is function `qsort1`.

Understand quicksort algorithm, unpacking keyword arguments with dictionaries and infinite code. 


Fifty Code Puzzles: 42 to 44

Understand quicksort algorithm, unpacking keyword arguments with dictionaries and infinite code.

Introduction

A Quick Overview of the Python Language

Fifty Code Puzzles

The Final Remarks

Puzzles 42 to 44

Puzzle 42

Quicksort