# 5 Best Ways to Convert a Python Set to a Sorted List

π‘ Problem Formulation: Developers often find themselves needing to organize unordered collections for various purposes. This article tackles the specific need to transform a Python set, an unordered collection of unique elements, into a sorted list. The input example could be a set like `{3, 1, 4, 1, 5, 9, 2}`, and the desired output a sorted list: `[1, 2, 3, 4, 5, 9]`.

## Method 1: Using the sorted() Function

The `sorted()` function in Python takes an iterable as an argument and returns a new sorted list from the elements of any iterable, which includes sets. It’s a direct and clear way to accomplish the task.

Here’s an example:

```my_set = {3, 1, 4, 1, 5, 9, 2}
sorted_list = sorted(my_set)
print(sorted_list)
```

Output:

`[1, 2, 3, 4, 5, 9]`

This code snippet starts with defining a set and then calls `sorted()` with the set as the argument, which returns a sorted list of the set’s elements, excluding any duplicates.

## Method 2: List Comprehension and sort()

List comprehension in Python provides a concise syntax for creating lists. Combine this with the `list.sort()` method to sort the list in place, and you have another method to convert a set to a sorted list.

Here’s an example:

```my_set = {3, 1, 4, 1, 5, 9, 2}
my_list = [i for i in my_set]
my_list.sort()
print(my_list)
```

Output:

`[1, 2, 3, 4, 5, 9]`

In this snippet, we create a list from the set using list comprehension, then use the `list.sort()` method to sort the list in place. This method ensures that the order of the list is changed to ascending.

## Method 3: Using heapq.merge()

The `heapq.merge()` function merges multiple sorted inputs into a single sorted output and returns an iterator over the sorted values. While primarily used for merging sorted iterables, it can be handy for converting a set to a sorted list too.

Here’s an example:

```import heapq
my_set = {3, 1, 4, 1, 5, 9, 2}
sorted_list = list(heapq.merge(my_set))
print(sorted_list)
```

Output:

`[1, 2, 3, 4, 5, 9]`

This method is a bit unconventional: `heapq.merge()` is used with a single set, and then the iterator is converted to a list. It’s not the most intuitive method for this task, but it works.

## Method 4: Using lambda and sorted()

A lambda function can serve as the `key` argument for the `sorted()` function, allowing for custom sort criteria. This might be overkill for simple element sorting but demonstrates flexibility.

Here’s an example:

```my_set = {3, 1, 4, 1, 5, 9, 2}
sorted_list = sorted(my_set, key=lambda x: x)
print(sorted_list)
```

Output:

`[1, 2, 3, 4, 5, 9]`

Though the lambda function used in this example is trivial, since it’s merely returning the value itself, it shows the process of using a lambda for potentially more complex sorting logic with the `sorted()` function.

## Bonus One-Liner Method 5: Using sorted() Directly in Print

If the goal is simply to display a sorted list from a set and not store it, a one-liner can be used directly in a print statement.

Here’s an example:

```my_set = {3, 1, 4, 1, 5, 9, 2}
print(sorted(my_set))
```

Output:

`[1, 2, 3, 4, 5, 9]`

This one-liner skips the assignment to a variable and calls `sorted()` directly within the print function, which demonstrates Python’s ability to nest function calls for brevity.

## Summary/Discussion

• Method 1: Using the sorted() Function. Strengths: Simple and direct. Weaknesses: none.
• Method 2: List Comprehension and sort(). Strengths: Teaches list comprehension; versatile. Weaknesses: Slightly verbose.
• Method 3: Using heapq.merge(). Strengths: Shows how to use merge function. Weaknesses: Overcomplicates the task.
• Method 4: Using lambda and sorted(). Strengths: Demonstrates flexibility with sorting criteria. Weaknesses: Overkill for simple sorting.
• Method 5: Using sorted() Directly in Print. Strengths: Quick and concise one-liner for output. Weaknesses: Does not store the result.