In this short post we will answer on the following questions:

  • What is set() in Python?
  • Is {} a set in Python?
  • Why would you use a Python set?
  • What is set structure in Python?

Quick answers

What is set() in Python?
set() is a built-in Python function used to create a set object. A set is a collection of unique, unordered elements.

Is {} a set in Python?
No. {} creates an empty dictionary, not a set. To create an empty set, you must use set().

Why would you use a Python set?
You use a set to store unique values, remove duplicates, perform fast membership checks, and apply mathematical set operations like union and intersection.

What is set structure in Python?
A set is an unordered, mutable, hash-based collection that only stores unique elements and does not support indexing.

What is set() in Python?

In Python, set() is used to create a new set object. A set stores only unique elements and automatically removes duplicates.

Example:

# create a set using set()
numbers = set([1, 2, 3, 4, 5])

# create a set using {}
letters = {'a', 'b', 'c', 'd'}

You can create a set from any iterable:

nums = set([1, 1, 2, 3])
print(nums)   # {1, 2, 3}

Is {} a set in Python?

No. {} creates an empty dictionary.

Correct way to create an empty set:

empty_set = set()

Incorrect (this is a dict):

not_a_set = {}

This is a common beginner mistake.

What is set structure in Python?

A Python set has these key characteristics:

  • Unordered (no index, no position)
  • Unique elements only
  • Mutable (you can add and remove items)
  • Implemented using a hash table
  • Very fast membership checks

Because sets are unordered, you cannot do this:

my_set[0]   # TypeError

result:

TypeError: 'set' object is not subscriptable

Why would you use a Python set?

Use a set when you need:

Remove duplicates

unique_items = set([1, 1, 2, 3])

Fast membership testing

if 5 in my_set:
    print("Found")

Mathematical set operations

A = {1, 2, 3}
B = {3, 4, 5}

A | B   # union
A & B   # intersection
A - B   # difference
A ^ B   # symmetric difference

Efficient filtering and comparisons between collections.

Common set methods

s.add(6)
s.remove(2)
s.discard(10)   # no error if missing
s.clear()

Summary

  • set() creates a set object
  • {} is a dictionary, not a set
  • Sets store only unique values
  • Sets are unordered and mutable
  • Sets are ideal for fast lookups and removing duplicates

Python sets are one of the most useful built-in data structures for performance and data cleaning tasks.

What is set() in Python? (detailed)

In Python, the set() function is used to create a new set object. A set is a collection of unique elements, meaning that it does not allow duplicate values. Sets are useful when you need to store a collection of unique items and perform operations such as intersection, union, and difference.

Here is an example of how to create a set in Python:

# creating a set using set() function
numbers = set([1, 2, 3, 4, 5])

# creating a set using {}
alphabets = {'a', 'b', 'c', 'd'}

You can also use set() to create a set from a list or any other iterable by passing it as an argument to the set() function.

numbers = set([1, 2, 3, 4, 5])

Sets are unordered collections, so the items have no index. This means that items have no order, so you can't access items by their index. And also sets are mutable, so you can add or remove elements from a set after it is created.

numbers.add(6)
numbers.remove(2)

You can also perform mathematical set operations like union, intersection, difference and symmetric difference on two or more sets.

A = {1, 2, 3, 4, 5}
B = {4, 5, 6, 7, 8}

# Union of A and B
print(A | B)

# Intersection of A and B
print(A & B)

# Difference of A and B
print(A - B)

# Symmetric Difference of A and B
print(A ^ B)

Why would you use a Python set? (detailed)

There are several reasons why you might use a set in Python:

  • Removing duplicates: Sets are useful for removing duplicate values from a collection. Since sets only store unique elements, you can easily convert a list or other iterable to a set to remove any duplicates.

  • Membership testing: Sets are very efficient for membership testing, meaning checking if an element is present in the set or not. Since sets are implemented using a hash table, the time complexity for membership testing is O(1) on average.

  • Mathematical set operations: Sets support mathematical set operations such as union, intersection, difference, and symmetric difference. These operations can be useful for comparing and combining sets of data.

  • Fast access: Sets have a fast access time, as they are implemented as a hash table. This makes them useful for large collections of items, where fast access is important.

  • Filtering : You can use sets to filter out the data in a python list, which is not present in the set.

  • Unordered collection: Sets are unordered collections, so the items have no index. This means that items have no order, so you can't access items by their index. This can be useful in some cases when the order of items is not important.

In summary, sets are useful in Python when you need a collection of unique items, fast membership testing, mathematical set operations, fast access to items, and when you don't need the order of items to be preserved.

Conclusion

In summary, the set() function creates a new set object, which is a collection of unique elements that can be modified and used for set operations.