Do you have a list but you want to convert it to a Python set? No problem! Use the set(...) constructor and pass the list object as an argument. For example, if you have a list of strings friends, you can convert it to a set using the call set(friends).

Here’s an example code snippet:

friends = ['Alice', 'Bob', 'Ann', 'Liz']

s = set(friends)

print(s)

# {'Ann', 'Alice', 'Bob', 'Liz'}

Try it yourself in our interactive Python shell:

Exercise: Add another string 'Alice' to the list friends and see the resulting set. How many elements do the list and the set have?

Python List to Set Time Complexity

The time complexity of converting a list to a set is linear in the number of list elements. So, if the set has n elements, the asymptotic complexity is O(n). The reason is that you need to iterate over each element in the list which is O(n), and add this element to the set which is O(1). Together the complexity is O(n) * O(1) = O(n * 1) = O(n).

Here’s the pseudo-code implementation of the list to set conversion method:

def list_to_set(l): s = set() # Repeat n times --> O(n) for x in l: # Add element to set --> O(1) s.add(x) return s friends = ['Alice', 'Bob', 'Ann', 'Liz', 'Alice']

s = list_to_set(friends)

print(s)

# {'Ann', 'Alice', 'Bob', 'Liz'}

Need help understanding this code snippet? Try visualizing it in your browser—just click “Next” to see what the code does in memory:

Python List to Set Remove Duplicates

The set data structure is one of the basic collection data types in Python and many other programming languages.

A set is an unordered collection of unique elements. (Read more on the Ultimate Guide to Python Sets)

• Collection: A set is a collection of elements like a list or a tuple. The collection consists of either primitive elements (e.g. integers, floats, strings), or complex elements (e.g. objects, tuples). However, in a set all data elements must be hashable because it heavily relies on the hash function to implement the specification.
• Unordered: Unlike lists, sets are unordered because there is no fixed order of the elements. In other words, regardless of the order you put stuff in the set, you can never be sure in which order the set stores these elements.
• Unique: All elements in the set are unique. Each pair of values (x,y) in the set produces a different pair of hash values (hash(x)!=hash(y)). Hence, each pair of elements x and y in the set are different.

Thus, you can remove all duplicates from a list x by converting it into a set and back into a list using the command list(set(x)). However, the ordering information may be lost in the process (as a set is, by definition, unordered).

friends = ['Alice', 'Bob', 'Ann', 'Liz', 'Alice', 'Bob']

print(friends)

# ['Alice', 'Bob', 'Ann', 'Liz', 'Alice', 'Bob'] dup_free = list(set(friends))

print(dup_free)

# ['Bob', 'Alice', 'Liz', 'Ann']

This way, the resulting list doesn’t have any duplicates—but it also has lost the order of elements: strings 'Liz' and 'Ann' switched their order after conversion. This may be different on your computer!

Python List to Set to List: list(set(x))

By converting a list x to a set and back to a list with the nested constructor expression list(set(x)), you achieve two things:

• You remove all duplicates from the original list x.
• You lose all ordering information. The resulting list may (or may not) have a complete new ordering of the remaining elements.

There’s no way out: the set data structure is more efficient than the list data structure only because it’s less powerful.

It’s like compressing an image: by removing information from the original image, the new image needs less resources on your computer at the cost of having a lower quality. If you convert the lossy-compressed image (or the set for that matter) back into the original data structure, it doesn’t look the same anymore.

This highlights an important trade-off in programming: always choose the right data structure for the particular problem at hand.

Python List to Set Preserve Order

But what if you want to preserve the order when converting a list to a set (and, maybe, back)? (You’d only do this to remove duplicates).

I’ve written a detailed article on this topic so check it out if you need more info.

Efficient Method: A shorter and more concise way is to create a dictionary out of the elements in the list to remove all duplicates and convert the dictionary back to a list. This preserves the order of the original list elements.

lst = ['Alice', 'Bob', 'Bob', 1, 1, 1, 2, 3, 3]

print(list(dict.fromkeys(lst)))

# ['Alice', 'Bob', 1, 2, 3]

1. Convert the list to a dictionary with dict.fromkeys(lst).
2. Convert the dictionary into a list with list(dict).

Each list element becomes a new key to the dictionary. For example, the list [1, 2, 3] becomes the dictionary {1:None, 2:None, 3:None}. All elements that occur multiple times will be assigned to the same key. Thus, the dictionary contains only unique keys—there cannot be multiple equal keys.

As dictionary values, you take dummy values (per default).

Then, you convert the dictionary back to a list, throwing away the dummy values.

Here’s the code:

>>> lst = [1, 1, 1, 3, 2, 5, 5, 2]

>>> dic = dict.fromkeys(lst)

>>> dic

{1: None, 3: None, 2: None, 5: None}

>>> duplicate_free = list(dic)

>>> duplicate_free

[1, 3, 2, 5]

This way, you can simply use the ordered dictionary data type.

Related blog articles:

• Python Remove Duplicates From List of Lists
• Python List Remove
• The Ultimate Guide to Python Dictionaries!

Python List to Set Error: Unhashable Type List

A common error is to try to convert a set to a list with unhashable data types. Here’s what happens if you try to convert a list of lists into a set:

users = [['Alice', 23, 'female'], ['Bob', 26, 'male'], ['Ann', 31, 'female']] s = set(users)

print(s)

The result is an error message unhashable type: 'list'.

'''

Traceback (most recent call last): File "C:\Users\xcent\Desktop\code.py", line 6, in <module> s = set(users)

TypeError: unhashable type: 'list' '''

Why are lists unhashable?

Because they are mutable: you can change a list by appending or removing elements. If you change the list data type, the hash value changes (it is calculated based on the content of the list). This directly violates the definition that a “hash value […] never changes during its lifetime” (see here).

Key takeaway: mutable data types are not hashable. Therefore, you cannot use them in sets.

So, how to solve it? Simply convert the inner lists into an immutable collection type such as a tuple:

users = [('Alice', 23, 'female'), ('Bob', 26, 'male'), ('Ann', 31, 'female')] s = set(users)

print(s)

# {('Bob', 26, 'male'),

# ('Ann', 31, 'female'),

# ('Alice', 23, 'female')}

Now, the result is a set of tuple elements. As tuples are immutable, the hash value will never change and you can create a set out of them.

Where to Go From Here?

Enough theory, let’s get some practice!

To become successful in coding, you need to get out there and solve real problems for real people. That’s how you can become a six-figure earner easily. And that’s how you polish the skills you really need in practice. After all, what’s the use of learning theory that nobody ever needs?

Practice projects is how you sharpen your saw in coding!

Do you want to become a code master by focusing on practical code projects that actually earn you money and solve problems for people?

Then become a Python freelance developer! It’s the best way of approaching the task of improving your Python skills—even if you are a complete beginner.

Join my free webinar “How to Build Your High-Income Skill Python” and watch how I grew my coding business online and how you can, too—from the comfort of your own home.

Join the free webinar now!

News | Bungie.net”> News | Bungie.net”>

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The International Game Developers Association has announced that it’s launching a new reporting-based initiative to curb bad industry behavior.

The system comes hand-in-hand with a new set of “standards” for the video game industry, which cover topics such as game crediting, crunch and management abuse, and “event diversity,” which covers representation among speakers at video game events.

Though this new reporting form marks a proactive step for a long-lived organization, an interview with Gamesindustry.biz notes the inherent limitations of such a reporting system, and that the organization’s goals aren’t exactly to publicly shame companies submitted through the process.

“Rehabilitation is better than punishment, in any context,” stated IGDA executive director Renee Gittins. “It’s less about creating an industry blacklist.”

The IGDA’s reporting plan does include some levers for external transparency. The announcement notes that anonymized versions of submitted reports can be accessed by the public and press about amonth after the IGDA has made an effort to notify the company reported in the form.

Additionally, Gittins states that the IGDA hopes to create a public database tracking these reports to keep developers aware about the conditions at different companies.

This isn’t the first time the IGDA has announced a ramp-up in efforts to combat bad industry behavior. In 2016, it came out swinging against top-down instituted crunch under Kate Edwards’ leadership. However, we’ve heard concerns from developers in the last few years that the IGDA still may not be properly equipped to curb bad behavior at these companies.

After all, by its own insistence, the IGDA is neither a trade union, a guild, or trade organization. It’s a non-profit whose primary purpose is advocating for game developers. Though this announcement is a major new step for the long-lived organization, only time will tell if its reporting system is able to enact change among industry bad actors.

Perchang has announced that it is on the lookout for beta testers for the upcoming strategy game, Warhammer Quest: Silver Tower. Based on the popular Games Workshop board game of the same name, Silver Tower doesn’t take place in the classic Warhammer Fantasy setting, but instead uses the Mortal Realms of Age of Sigmar. In a similar vein to other Warhammer games like Vermintide or Chaosbane, Silver Tower revolves around a band of heroes from a variety of different races who make their home in the world.

Each of these heroes has a particular combat focus, so it’s safe to say that the Fyreslayer – the axe wielding Dwarf we see in the trailer – is a melee blender, whereas the armoured and shielded Stormcast will more likely trend towards tankiness.

The campaign sees you and your heroes face off against monsters from throughout the realms, as the Gaunt Summoner – who we guess is that guy with all the eyes – challenges you to a number of trials. Silver Tower will launch with over 100 stages to play, so you’ll have no problem finding foes to crush.

Warhammer Quest: Silver Tower has ten upgradable heroes, but we’re really excited to see how a Warhammer game using Age of Sigmar as a setting might change up the usual Warhammer hero roster of elf, human, wizard, and dwarf.

Alongside the trials set by that Tzeentch-y looking dude with the eyes, there are challenges and trials to complete, and even full-on solo trials for those of you who actually want to punish yourselves – hey, who are we to judge?

If that all sounds good, you can register interest for the beta by popping an email over to [email protected] A member of the team will then get back to you providing beta details, then fingers crossed, you’ll be a Sigmarine stomping on daemon spawn in no time. Praise the emper- I mean Sigmar.

“We discovered some issues that came up and are needing some additional QA time with the build as we want to make sure we get something out that is thoroughly vetted on our end. PTR will not be going live today due to these additional tests needed....”https://t.co/xWX0a0nzrp

— Diablo (Season 20 is LIVE) (@Diablo) May 21, 2020

One classic game that’s made a comeback during the Switch generation is Blaster Master, thanks to the release of Blaster Master Zero and Blaster Master Zero 2. We loved both entries in our reviews, and while we’d often tell you to go and play them right away if you haven’t already, in this case we’re going to advise you hold off just a little longer.

You see, the physical specialist Limited Run Games recently took to Twitter to tease some sort of Blaster Master announcement for next Monday. Take a look below:

The artwork appears to be based on the Zero entries, so we’re guessing it’ll be some sort of physical release tied to either one or both of these games. A lot of fans are also requesting a double pack as well. Whatever the announcement is, we just hope it involves the Nintendo Switch.

What do you think LRG is teasing? Have you bought any of its physical releases before? Share your thoughts down below.