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# Python set operation.

In mathematics, a set is a collection of distinct objects, considered as an object in its own right. For example, the numbers 2, 4, and 6 are distinct objects when considered separately, but when they are considered collectively they form a single set of size three, written {2,4,6}.

## Operations on Sets

Operation | Notation | Meaning |
---|---|---|

Intersection | A ∩ B | all elements which are in both and |

Union | A ∪ B | all elements which are in either or (or both) |

Difference | A − B | all elements which are in but not in |

Complement | (or) | all elements which are not in |

In python, compared to list, the main advantages of using a set are that it has optimized functions for checking whether a specific element is a member of the set or not. This is based on a hash table data structure.

## Methods for Sets

**add(x) Method:** It adds the item x to a set if it is non-preexisting.

A = {"AA", "BB", "CC"} A.add("VV")

This will add VV in A set.

**union(s) Method:** It returns a union of two set.Using the operator ‘|’between 2 existing sets is the same as writing My_Set1.union(My_Set2)..

A = {"AA", "BB", "CC"} B = {"MM", "NN"} Z = A.union(B) OR Z = A|B

Set population set will have components of both A and B.

**intersect(s) Method:** It returns an intersection of two givensets. The ‘&’ operator can be used in this operation.

S = A.intersection(B)

Set victims will contain the common elements of A and B.

**difference(s) Method:** Returns a set containing all the elements which are existing in the first set but not present in the second set. We can use ‘-‘ operator here.

W = A.difference(B) OR S = A – B

Set safe will have all the elements that are in A but not in B.

**clear() Method:** The whole existing set will become empty.

B.clear()

Clears B set

## Operators for Sets

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 s1 ˆ s2 # the set of elements in precisely one of s1 or s2

## Example Code

# Python program to demonstrate working# of # Set in Python # creating two sets My_Set1 = set() My_Set2 = set() # Adding elements to My_Set1 for i in range(1, 6): My_Set1.add(i) # Adding elements to My_Set2 for i in range(3, 8): My_Set2.add(i) print("My_Set1 = ", My_Set1) print("My_Set2 = ", My_Set2) print("\n") # Union of My_Set1 and My_Set2 My_Set3 = My_Set1 | My_Set2# My_Set1.union(My_Set2) print("Union of My_Set1&My_Set2: My_Set3 = ", My_Set3) # Intersection of My_Set1 and My_Set2 My_Set4 = My_Set1&My_Set2# My_Set1.intersection(My_Set2) print("Intersection of My_Set1&My_Set2: My_Set4 = ", My_Set4) print("\n") # Checking relation between My_Set3 and My_Set4 if My_Set3>My_Set4: # My_Set3.issuperset(My_Set4) print("My_Set3 is superset of My_Set4") elif My_Set3<My_Set4: # My_Set3.issubset(My_Set4) print("My_Set3 is subset of My_Set4") else : # My_Set3 == My_Set4 print("My_Set3 is same as My_Set4") # displaying relation between My_Set4 and My_Set3 if My_Set4<My_Set3: # My_Set4.issubset(My_Set3) print("My_Set4 is subset of My_Set3") print("\n") # difference between My_Set3 and My_Set4 My_Set5 = My_Set3 - My_Set4 print("Elements in My_Set3 and not in My_Set4: My_Set5 = ", My_Set5) print("\n") # check if My_Set4 and My_Set5 are disjoint sets if My_Set4.isdisjoint(My_Set5): print("My_Set4 and My_Set5 have nothing in common\n") # Removing all the values of My_Set5 My_Set5.clear() print("After applying clear on sets My_Set5: ") print("My_Set5 = ", My_Set5)

## Output

My_Set1 = {1, 2, 3, 4, 5} My_Set2 = {3, 4, 5, 6, 7} Union of My_Set1&My_Set2: My_Set3 = {1, 2, 3, 4, 5, 6, 7} Intersection of My_Set1&My_Set2: My_Set4 = {3, 4, 5} My_Set3 is superset of My_Set4 My_Set4 is subset of My_Set3 Elements in My_Set3 and not in My_Set4: My_Set5 = {1, 2, 6, 7} My_Set4 and My_Set5 have nothing in common After applying clear on sets My_Set5: My_Set5 = set()

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