Python Set Tutorial – Creation, Operations, and Usage

Python includes a built‑in data type called set , which represents an unordered collection of unique elements and supports membership testing, duplicate elimination, and mathematical operations such as union, intersection, difference, and symmetric difference.

Creating Sets

Sets can be created using curly braces or the set() function. The argument to set() must be an iterable (e.g., list, tuple, dictionary). Because sets discard duplicates, they are useful for deduplicating strings, lists, or tuples.

1. Creating an empty set

<code>&gt;&gt; s = set()
&gt;&gt; s
set()
&gt;&gt; s1 = set([])  # list
&gt;&gt; s1
set()
&gt;&gt; s2 = set(())  # tuple
&gt;&gt; s2
set()
&gt;&gt; s3 = set({})  # dictionary
&gt;&gt; s3
set()</code>

Note: Use set() for an empty set; {} creates an empty dictionary.

2. Creating a non‑empty set

<code>&gt;&gt; s1 = set([1, 2, 3, 4])
&gt;&gt; s1
{1, 2, 3, 4}
&gt;&gt; s3 = set({'a': 2, 'b': 3, 'c': 4})
&gt;&gt; s3
{'c', 'a', 'b'}</code>

When converting a dictionary to a set, only the keys are taken.

Set Operations

1. Adding Elements

add() inserts a single element as a whole:

<code>&gt;&gt; s = set('one')
&gt;&gt; s
{'e', 'o', 'n'}
&gt;&gt; s.add('two')
&gt;&gt; s
{'e', 'two', 'o', 'n'}</code>

update() iterates over the supplied iterable and adds each element individually, removing duplicates:

<code>&gt;&gt; s = set('one')
&gt;&gt; s.update('two')
&gt;&gt; s
{'e', 'n', 't', 'w', 'o'}</code>

2. Removing Elements

setVar.remove(element) deletes element and raises a KeyError if it is absent.

<code>&gt;&gt; s = set('one')
&gt;&gt; s.remove('e')
&gt;&gt; s
{'n', 'o'}</code>

setVar.discard(element) also deletes element but does nothing if the element is not present.

<code>&gt;&gt; sList = set([1, 2, 3, 4, 5])
&gt;&gt; sList.discard(1)
&gt;&gt; sList
{2, 3, 4, 5}</code>

s.pop() removes and returns an arbitrary element, raising KeyError when the set is empty.

<code>&gt;&gt; sList = {2, 3, 4, 5}
&gt;&gt; sList.pop()
2</code>

s.clear() empties the set.

<code>&gt;&gt; sList.clear()
&gt;&gt; sList
set()</code>

3. Iterating Over a Set

Iteration works like any other iterable:

<code>&gt;&gt;&gt; s = set('one')
&gt;&gt;&gt; for i in s:
...     print(i)
 e
 o
 n
&gt;&gt;&gt; for index, i in enumerate(s):
...     print(index, i)
0 e
1 o
2 n</code>

4. Set Algebra Operators

Intersection ( & ), union ( | ), and difference ( - ) use familiar symbols:

<code># Intersection
&gt;&gt; st1 = set('python')
&gt;&gt; st2 = set('htc')
&gt;&gt; st1 &amp; st2
{'h', 't'}
# Union
&gt;&gt; st3 = set('two')
&gt;&gt; st1 | st3
{'p', 't', 'w', 'y', 'h', 'o', 'n'}
# Difference
&gt;&gt; st1 - set('4589')
{'1', '3', '2', '7', '6'}</code>

The difference() method provides the same result as the subtraction operator.

Set Comparison

Sets can be compared using > , >= , < , <= , == , and != to test subset/superset relationships and equality.

<code>&gt;&gt;&gt; s1 = set([1, 2, 3, 4, 5])
&gt;&gt;&gt; s2 = set([1, 2, 3, 4])
&gt;&gt;&gt; s1 &gt; s2
True
&gt;&gt;&gt; s1 == s2
False
&gt;&gt;&gt; s1 != s2
True</code>

Immutable Sets – frozenset

The frozenset type is an immutable version of set ; its contents cannot be changed after creation.

<code>&gt;&gt; f = frozenset()
&gt;&gt; f
frozenset([])
&gt;&gt; f = frozenset('asdf')
&gt;&gt; f
frozenset({'a', 's', 'd', 'f'})
&gt;&gt; f = frozenset([1, 2, 3, 4])
&gt;&gt; f
frozenset({1, 2, 3, 4})</code>

These immutable sets can be used as dictionary keys or elements of other sets.