# Set is mathematical set: NO duplicates
#
# It is also NOT indexable

s = set()
s.add(1) # s is now { 1 }
s.add(2) # s is now { 1, 2 }
s.add(2) # s is still { 1, 2 }
x = len(s) # equals 2

# Membership test:

y = 2 in s # equals True
z = 3 in s # equals False


# We’ll use sets for two main reasons. 

# (1) The first is that in is a very fast test operation on sets. 
#
#     If we have a large collection of items that we want to use 
#     for a membership test, a set is more appropriate than a list

# (2) The second reason is to find (construct) the distinct items 
#     in a collection:

item_list = [1, 2, 3, 1, 2, 3]
num_items = len(item_list) # 6
item_set = set(item_list) # {1, 2, 3}

num_distinct_items = len(item_set) # 3
distinct_item_list = list(item_set) # [1, 2, 3]