Set to list python

Set to list python

Given a set, write a Python program to convert the given set into list.


Approach #1 : Using list(set_name) .

Typecasting to list can be done by simply using list(set_name) .

Approach #2 : using sorted() method

Using sorted() function will convert the set into list in a defined order. The only drawback of this method is that the elements of the set need to be sortable.

Approach #3 : Using [*set, ]
This essentially unpacks the set s inside a list literal which is created due to the presence of the single comma (, ). This approach is a bit faster but suffers from readability.

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I am trying to convert a set to a list in Python 2.6. I’m using this syntax:

However, I get the following stack trace:

How can I fix this?

9 Answers 9

It is already a list

Do you want something like

EDIT : Output of your last comment

I’m wondering if you did something like this :

Why not shortcut the process:

This will remove the dupes from you list and return a list back to you.

[EDITED] It’s seems you earlier have redefined "list", using it as a variable name, like this:

Whenever you are stuck in such type of problems, try to find the datatype of the element you want to convert first by using :

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to convert it to a list. You can use the newly built list like any normal list in python now.

Review your first line. Your stack trace is clearly not from the code you’ve pasted here, so I don’t know precisely what you’ve done.

What you wanted was set([1, 2, 3, 4]) .

The "not callable" exception means you were doing something like set()() — attempting to call a set instance.

This will turn a set in the form <‘1′,’2’>into a list in the form [‘1′,’2’].

I’m not sure that you’re creating a set with this ([1, 2]) syntax, rather a list. To create a set, you should use set([1, 2]) .

These brackets are just envelopping your expression, as if you would have written:

There’re not really ignored, but do nothing to your expression.

Note: (something, something_else) will create a tuple (but still no list).

Python is a dynamically typed language, which means that you cannot define the type of the variable as you do in C or C++:

In Python, you use coercing if you change types, or the init functions (constructors) of the types to declare a variable of a type:

In this tutorial, we’ll discover two Pythonic ways to find the Difference Between Two Lists. One of the methods is using the Python Set. It first converts the lists into sets and then gets the unique part out of that.

Other non-set methods compare two lists element by element and collect the unique ones. We can implement these by using nested for loops and with the list comprehension.

By the way, if you are not aware of the sets in Python, then follow the below tutorial. It would quickly introduce you to how Python implements the mathematical form of Set.

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Pythonic Ways to Find the Difference Between Two Lists

Python Set seems to be the most obvious choice to identify the common as well as the difference of two lists. So, we are going to explore it first and then will use nested loops and list comprehension.

Before we move on to the solution part, let’s define the test parameters, i.e., the two lists which we have to find the difference.

And we want our solution to provide the following output:

Let’s start to create a program to find the difference between two lists, first using sets.

Use set() to find the difference of two lists

In this approach, we’ll first derive two SETs (say set1 and set2) from the LISTs (say list1 and list2) by passing them to set() function. After that, we’ll perform the set difference operation. It will return those elements from list1 which don’t exist in the second.

Here is the sample Python program to get the difference of two lists.

After running this, you should see the following outcome:

Without set(), using nested loops

In this method, we’ll use nested For Loop to compare each element of the first list with the second. And while traversing, we’ll be appending every non-matching item to a new (and empty) list.

The new list would finally include the difference between the two given sequences. Below is the sample program to demonstrate this approach.

After running the above program, you should see the following outcome:

Without set(), using list comprehension

It is almost a similar technique that we used in the previous one. Here, we replaced the nested loops with the list comprehension syntax.

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See the example below.

After running the above program, you should see the following outcome:

We hope that after wrapping up this tutorial, you should know several ways to check two lists for the difference. However, you may practice more with examples to gain confidence.

Also, to learn Python from scratch to depth, do read our step by step Python tutorial .

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