Sets
Sets are data structures, similar to lists or dictionaries. They are created using curly braces, or the set function. They share some functionality with lists, such as the use of in to check whether they contain a particular item.
num_set = {1, 2, 3, 4, 5}
word_set = set(["spam", "eggs", "sausage"])
print(3 in num_set)
print("spam" not in word_set)
To create an empty set, you must use set(), as {} creates an empty dictionary.
Sets differ from lists in several ways, but share several list operations such as len.
few properties of set
- They are unordered, which means that they can’t be indexed.
- They cannot contain duplicate elements.
- Due to the way they’re stored, it’s faster to check whether an item is part of a set, rather than part of a list.
- Instead of using append() to add to a set, use add().
- The method remove() removes a specific element from a set; pop() removes an arbitrary element.
nums = {1, 2, 1, 3, 1, 4, 5, 6}
print(nums)
nums.add(-7)
nums.remove(3)
print(nums)
Note: Basic uses of sets include membership testing and the elimination of duplicate entries.
Set operations
- Sets can be combined using mathematical operations.
- The union operator | combines two sets to form a new one containing items in either.
- The intersection operator & gets items only in both.
- The difference operator – gets items in the first set but not in the second.
- The symmetric difference operator ^ gets items in either set, but not both.
first = {1, 2, 3, 4, 5, 6}
second = {4, 5, 6, 7, 8, 9}
print(first | second)
print(first & second)
print(first - second)
print(second - first)
print(first ^ second)
DForDataScience.com 