[Tut] How to Sort and Return a Python List in One Line?

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How to Sort and Return a Python List in One Line?

To sort and return a Python list in a single line of code, use the

Code:

sorted(list)

method that returns a new list of sorted elements. It copies only the references to the original elements so the returned list is not a deep but a shallow copy.



Let’s dive into the challenge to learn about more details and alternatives. Everything is not always simple. By studying the different methods that solves this, you’ll become a better coder!

Problem: Given a listof comparable objects such as integers or floats. Is there a way to sort the list and return the sorted list in a single line of Python code?

Example: Say, you’ve got the following list.

Code:

a = [4, 2, 1, 3]

You want to sort this list and return the result in a single line. If you use the

Code:

list.sort()

method, the return value is

Code:

None

:

Code:

print(a.sort()) # None

The return value of the

Code:

list.sort()

method is

Code:

None

, but many coders expect it to be the sorted list. So they’re surprised finding out that their variables contain the

Code:

None

type rather than a sorted list.

However, returning

Code:

None

makes perfect sense for the

Code:

list.sort()

method. Why? Because you call the method on a list objectand it modifies this exact list object. It doesn’t create a new list—there won’t be a new list object in memory.

So, how to sort and return a list in a single line of Python code? As a rule of thumb, there are always multiple ways to accomplish the same thing in Python. Let’s dive into the different ways to accomplish this!

Here’s a quick overview of the methods addressed in this article:

https://repl.it/@finxter/ModestAllMp3?lite=true

Exercise: Change the list to be sorted by adding negative floats. Does it still work?

You’ll now learn more about each of the methods.

Method 1: sorted()

The easiest way to accomplish this task is to call Python’s built-in

Code:

sorted()

function that takes an iterable and returns a new list with sorted elements.

Code:

a = [4, 2, 1, 3] # Method 1: sorted() print(sorted(a))

The

Code:

sorted()

function generates a new sorted list that is put into the

Code:

print()

function that prints the sorted list to the shell. The output is the sorted list:

Code:

[1, 2, 3, 4]

This method is the most Pythonicone. But are there alternatives?

Method 2: list.sort() + Ternary Operator

The

Code:

sorted()

method leaves the original list unchanged. But what if you want to sort the original list and get this original list as an output that you can assign to a variable?

The answer is simple: use a combination of the

Code:

list.sort()

method and the ternary operator!

Code:

a = [4, 2, 1, 3] # Method 2: list.sort() + ternary print(a if a.sort() else a) # [1, 2, 3, 4]

You need to understand two concepts: (1)

Code:

list.sort()

and (2) the ternary operator:

1. The
   Code:

   list.sort()
   method sorts the list elements in place in an ascending manner. To customize the default sorting behavior, use the optional
   Code:

   key
   argument by passing a functionthat returns a comparable value for each element in the list.
   
   
2. The ternary operator
   Code:

   x if c else y
   consists of three operands
   Code:

   x
   ,
   Code:

   c
   , and
   Code:

   y
   . It returns
   Code:

   x
   if the Boolean expression
   Code:

   c
   evaluates to
   Code:

   True
   . Otherwise, if the expression
   Code:

   c
   evaluates to
   Code:

   False
   , the ternary operator returns the alternative
   Code:

   y
   .
   

The beautiful thing is that the one-liner

Code:

print(a if a.sort() else a)

modifies the original list and returns it right away. How does it do this?

Explanation: First, the

Code:

a.sort()

method is called to check which “branch” of the ternary operator should be visited. The return value of

Code:

a.sort()

will always be

Code:

None

. The

Code:

None

value is automatically converted to the Boolean

Code:

False

. Thus, the ternary operator always returns the list object referred to by variable

Code:

a

.

Note that the only purpose of the ternary operator is to make sure to call the

Code:

a.sort()

method before returning the value

Code:

a

—to make sure it is sorted!

If you print the original list to the shell, you’ll see that it is now sorted:

Code:

>>> print(a) [1, 2, 3, 4]

Method 3: Combining Multiple Statements in a Single Line with Semicolon

An alternative is chaining the statements with a semicolon

Code:

;

to one-linerize a Python code snippet. This strategy works with flat Python programs without, possible nested, blocks:

Code:

a = [4, 2, 1, 3] # Method 3: semicolon a.sort(); print(a) # [1, 2, 3, 4]

If you need to sort a Python list and print its return value to the shell—for example because you run this command from the command line or terminal—you can use this excellent strategy.

You can learn more about how to one-linerize any Python program in my following video:



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