A set in Python is an unordered collection of unique elements. Sets are perfect when you want to eliminate duplicates or perform mathematical set operations like union, intersection, and difference.
In this tutorial, you’ll learn:
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What sets are
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How to create and use them
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Set operations and methods
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Common use cases
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Tips and pitfalls
What Is a Set?
A set is:
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Unordered (no indexing)
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Unchangeable (elements can't be changed, but items can be added/removed)
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No duplicate elements
Creating a Set
my_set = {1, 2, 3}
print(my_set) # {1, 2, 3}
Creating an Empty Set
Important:
{}creates an empty dictionary, not a set.
empty_set = set()
Mixed Data Types Allowed
mixed_set = {"apple", 42, True}
Accessing Set Items
Since sets are unordered, you can’t access items by index.
Instead, loop through:
for item in my_set:
print(item)
Set Methods
| Method | Description | Example |
|---|---|---|
add() |
Adds a single item | my_set.add(4) |
update() |
Adds multiple items | my_set.update([4, 5]) |
remove() |
Removes item, errors if not found | my_set.remove(2) |
discard() |
Removes item, no error if not found | my_set.discard(99) |
pop() |
Removes a random item | my_set.pop() |
clear() |
Empties the set | my_set.clear() |
copy() |
Copies the set | new_set = my_set.copy() |
Set Operations
Sets shine in performing mathematical operations:
✅ Union
Combines all unique elements from both sets.
a = {1, 2, 3}
b = {3, 4, 5}
print(a.union(b)) # {1, 2, 3, 4, 5}
✅ Intersection
Common elements in both sets.
print(a.intersection(b)) # {3}
✅ Difference
Items in one set but not the other.
print(a.difference(b)) # {1, 2}
✅ Symmetric Difference
Items not common to both.
print(a.symmetric_difference(b)) # {1, 2, 4, 5}
Checking Set Relationships
| Operation | Description | Example |
|---|---|---|
issubset() |
Is a a subset of b? |
a.issubset(b) |
issuperset() |
Is a a superset of b? |
a.issuperset(b) |
isdisjoint() |
No common elements? | a.isdisjoint(b) |
❗ Duplicates are Automatically Removed
numbers = {1, 2, 2, 3, 4, 4}
print(numbers) # {1, 2, 3, 4}
Frozenset: Immutable Set
A frozenset is a set that cannot be changed after creation.
frozen = frozenset([1, 2, 3])
# frozen.add(4) → ❌ Error
Useful when you need to use sets as dictionary keys or protect data from being modified.
Example: Remove Duplicates from a List
my_list = [1, 2, 2, 3, 4, 4, 5]
unique = list(set(my_list))
print(unique) # [1, 2, 3, 4, 5]
Example: Set Operations Demo
a = {1, 2, 3}
b = {3, 4, 5}
print("Union:", a | b)
print("Intersection:", a & b)
print("Difference:", a - b)
print("Symmetric Difference:", a ^ b)
Tips for Using Sets
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Use sets to eliminate duplicates from lists.
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Use
update()instead of looping to add multiple elements. -
Use
discard()instead ofremove()if you're unsure if the item exists. -
Convert strings/lists to sets to do fast membership tests.
⚠️ Common Pitfalls
| Pitfall | Explanation | Fix |
|---|---|---|
{} creates dict |
Use set() for empty set |
empty = set() |
| Unordered | You can’t access by index | Use a list if ordering matters |
remove() errors if item not found |
Use discard() instead |
my_set.discard("value") |
| Sets can’t contain mutable types | Can’t add lists/dicts to a set | Use tuples/frozensets if needed |
Summary
| Feature | Description |
|---|---|
| Type | set |
| Ordered? | ❌ No |
| Changeable? | ✅ Yes (items can be added/removed) |
| Allows Duplicates? | ❌ No |
| Use Case | Unique elements, fast membership testing |
✅ Practice Exercise
Task: Write a function that returns common items between two lists using sets.
def common_elements(list1, list2):
return list(set(list1) & set(list2))
a = [1, 2, 3, 4]
b = [3, 4, 5, 6]
print(common_elements(a, b)) # [3, 4]
What's Next?
Now that you’ve mastered sets, explore:
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Dictionaries (key-value structures)
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List comprehensions with sets
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Performance comparison:
inwith lists vs. sets
Tips and Tricks
What is pass in Python?
Python | Pass Statement
The pass statement is used as a placeholder for future code. It represents a null operation in Python. It is generally used for the purpose of filling up empty blocks of code which may execute during runtime but has yet to be written.
def myfunction():
pass
How can you generate random numbers?
Python | Generate random numbers
Python provides a module called random using which we can generate random numbers. e.g: print(random.random())
We have to import a random module and call the random() method as shown below:
import random
print(random.random())
The random() method generates float values lying between 0 and 1 randomly.
To generate customized random numbers between specified ranges, we can use the randrange() method
Syntax: randrange(beginning, end, step)
import random
print(random.randrange(5,100,2))
What is lambda in Python?
Python | Lambda function
A lambda function is a small anonymous function. This function can have any number of parameters but, can have just one statement.
Syntex:
lambda arguments : expression
a = lambda x,y : x+y
print(a(5, 6))
It also provides a nice way to write closures. With that power, you can do things like this.
def adder(x):
return lambda y: x + y
add5 = adder(5)
add5(1) #6
As you can see from the snippet of Python, the function adder takes in an argument x and returns an anonymous function, or lambda, that takes another argument y. That anonymous function allows you to create functions from functions. This is a simple example, but it should convey the power lambdas and closures have.
What is swapcase() function in the Python?
Python | swapcase() Function
It is a string's function that converts all uppercase characters into lowercase and vice versa. It automatically ignores all the non-alphabetic characters.
string = "IT IS IN LOWERCASE."
print(string.swapcase())
How to remove whitespaces from a string in Python?
Python | strip() Function | Remove whitespaces from a string
To remove the whitespaces and trailing spaces from the string, Python provides a strip([str]) built-in function. This function returns a copy of the string after removing whitespaces if present. Otherwise returns the original string.
string = " Python "
print(string.strip())
What is the usage of enumerate() function in Python?
Python | enumerate() Function
The enumerate() function is used to iterate through the sequence and retrieve the index position and its corresponding value at the same time.
lst = ["A","B","C"]
print (list(enumerate(lst)))
#[(0, 'A'), (1, 'B'), (2, 'C')]
Can you explain the filter(), map(), and reduce() functions?
Python | filter(), map(), and reduce() Functions
- filter() function accepts two arguments, a function and an iterable, where each element of the iterable is filtered through the function to test if the item is accepted or not.
>>> set(filter(lambda x:x>4, range(7))) # {5, 6}
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map() function calls the specified function for each item of an iterable and returns a list of result
>>> set(map(lambda x:x**3, range(7))) # {0, 1, 64, 8, 216, 27, 125}
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reduce() function reduces a sequence pair-wise, repeatedly until we arrive at a single value..
>>> reduce(lambda x,y:y-x, [1,2,3,4,5]) # 3Let’s understand this:
2-1=1
3-1=2
4-2=2
5-2=3Hence, 3.
What is a namedtuple?
Python | namedtuple
A namedtuple will let us access a tuple’s elements using a name/label. We use the function namedtuple() for this, and import it from collections.
>>> from collections import namedtuple
#format
>>> result=namedtuple('result','Physics Chemistry Maths')
#declaring the tuple
>>> Chris=result(Physics=86,Chemistry=92,Maths=80)
>>> Chris.Chemistry
# 92
Write a code to add the values of same keys in two different dictionaries and return a new dictionary.
We can use the Counter method from the collections module
from collections import Counter
dict1 = {'a': 5, 'b': 3, 'c': 2}
dict2 = {'a': 2, 'b': 4, 'c': 3}
new_dict = Counter(dict1) + Counter(dict2)
print(new_dict)
# Print: Counter({'a': 7, 'b': 7, 'c': 5})
Python In-place swapping of two numbers
Python | In-place swapping of two numbers
>>> a, b = 10, 20
>>> print(a, b)
10 20
>>> a, b = b, a
>>> print(a, b)
20 10
Reversing a String in Python
Python | Reversing a String
>>> x = 'PythonWorld'
>>> print(x[: : -1])
dlroWnohtyP
Python join all items of a list to convert into a single string
Python | Join all items of a list to convert into a single string
>>> x = ["Python", "Online", "Training"]
>>> print(" ".join(x))
Python Online Training
python return multiple values from functions
Python | Return multiple values from functions
>>> def A():
return 2, 3, 4
>>> a, b, c = A()
>>> print(a, b, c)
2 3 4
Python Print String N times
Python | Print String N times
>>> s = 'Python'
>>> n = 5
>>> print(s * n)
PythonPythonPythonPythonPython
Python check the memory usage of an object
Python | Check the memory usage of an object
>>> import sys
>>> x = 100
>>> print(sys.getsizeof(x))
28
