SETS

What are sets?

Set is an unordered collection of unique items. Set is defined by values separated by comma inside braces { }. Items in a set are not ordered.

Why use sets?

Set have unique values. They eliminate duplicates. Python’s set class represents the mathematical notion of a set. The elements in the set are immutable(cannot be modified) but the set as a whole is mutable. The major advantage of using a set, as opposed to a list, is that it has a highly optimized method for checking whether a specific element is contained in the set.

Python Frozenset

Frozenset is a new class that has the characteristics of a set, but its elements cannot be changed once assigned. This datatype supports methods like difference(), intersection(), union(), etc. Being immutable it does not have method that add or remove elements.

Methods for Sets

1. add(x) and update(x) Method:

We can add single element using the add() method and multiple elements using the update()method. The update() method can take tuples, lists, strings or other sets as its argument.

Eg.people = {"Jay", "Idrish", "Archil"} people.add("Daxit")

2. union(s) Method:

Returns a union of two set.Using the ‘|’ operator between 2 sets is the same as writing set1.union(set2) Eg. people = {"Jay", "Idrish", "Archil"} vampires = {"Karan", "Arjun"} population = people.union(vampires) you could also use population = people|vampires

3.intersect(s) Method:

Returns an intersection of two sets.The ‘&’ operator can also be used in this case. victims = people.intersection(vampires) you could also use victims=people & vampires

4. difference(s) Method:

Returns a set containing all the elements of invoking set but not of the second set. We can use ‘-‘ operator here. safe = people.difference(vampires) you can also use safe= people – vampires

5. clear() Method:

Empties the whole set. victims.clear()

Sets and frozen sets support the following operators:

key in s #containment check

key not in s #non-containment check

s1 == s2 #s1 is equivalent to s2

s1 != s2 #s1 is not equivalent to s2

s1 <= s2 #s1is subset of s2 s1 < s2 # s1 is proper subset of s2 s1 >= s2 # s1is superset of s2

s1 > s2 #s1 is proper superset of s2

s1 | s2 #the union of s1 and s2

s1 & s2 #the intersection of s1 and s2

s1 – s2 #the set of elements in s1 but not s2