Sets in python

A set is an unordered collection of zero or more immutable Python data objects. Sets do not allow duplicates and are written as comma-delimited values enclosed in curly braces. The empty set is represented by set(). Sets are heterogeneous, and the collection can be assigned to a variable as below.

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>>> {3,6,"cat",4.5,False} {False, 4.5, 3, 6, 'cat'} >>> mySet = {3,6,"cat",4.5,False} >>> mySet {False, 4.5, 3, 6, 'cat'} >>>

Even though sets are not considered to be sequential, they do support a few of the familiar operations presented earlier. Table  reviews these operations and the following session gives examples of their use.

Operation Name	Operator	Explanation
membership	in	Set membership
length	len	Returns the cardinality of the set
|	aset | otherset	Returns a new set with all elements from both sets
&	aset & otherset	Returns a new set with only those elements common to both sets
-	aset - otherset	Returns a new set with all items from the first set not in second
<=	aset <= otherset	Asks whether all elements of the first set are in the second

Operations on a Set in Python

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>>> mySet {False, 4.5, 3, 6, 'cat'} >>> len(mySet) 5 >>> False in mySet True >>> "dog" in mySet False >>>

Sets support a number of methods that should be familiar to those who have worked with them in a mathematics setting. Table  provides a summary. Examples of their use follow. Note that union, intersection, issubset, and difference all have operators that can be used as well.

Method Name	Use	Explanation
union	aset.union(otherset)	Returns a new set with all elements from both sets
intersection	aset.intersection(otherset)	Returns a new set with only those elements common to both sets
difference	aset.difference(otherset)	Returns a new set with all items from first set not in second
issubset	aset.issubset(otherset)	Asks whether all elements of one set are in the other
add	aset.add(item)	Adds item to the set
remove	aset.remove(item)	Removes item from the set
pop	aset.pop()	Removes an arbitrary element from the set
clear	aset.clear()	Removes all elements from the set

aset.clear()

Removes all elements from the set

Methods Provided by Sets in Python

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>>> mySet {False, 4.5, 3, 6, 'cat'} >>> yourSet = {99,3,100} >>> mySet.union(yourSet) {False, 4.5, 3, 100, 6, 'cat', 99} >>> mySet | yourSet {False, 4.5, 3, 100, 6, 'cat', 99} >>> mySet.intersection(yourSet) {3} >>> mySet & yourSet {3} >>> mySet.difference(yourSet) {False, 4.5, 6, 'cat'} >>> mySet - yourSet {False, 4.5, 6, 'cat'} >>> {3,100}.issubset(yourSet) True >>> {3,100}<=yourSet True >>> mySet.add("house") >>> mySet {False, 4.5, 3, 6, 'house', 'cat'} >>> mySet.remove(4.5) >>> mySet {False, 3, 6, 'house', 'cat'} >>> mySet.pop() False >>> mySet {3, 6, 'house', 'cat'} >>> mySet.clear() >>> mySet set() >>>

 From:http://interactivepython.org/courselib/static/pythonds/Introduction/introduction.html

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