s = set() # empty set (no literal syntax for empty set)

s = {1,2,3}

2 in s # True O(1)

del s

{1,2,3} == set([1,2,3]) # True

s = {1,2,3}

s.add('foo') # {1,2,3,'foo'}

s.update({'bar',4}) # {1,2,3,4,'foo','bar'}

s.update([5,6]) # {1,2,3,4,5,'foo',6,'bar'}

s.remove(5) # {1,2,3,4,'foo',6,'bar'}

s.remove(5) # err

s.discard(4) # {1,2,3,'foo',6,'bar'}

s.discard(4) # no err

s.pop() # {2,3,'foo',6,'bar'} note: can't know which item gets poped (since sets are unordered)

s.clear() # {}

{1,2}.copy() # {1,2}

{1,2}.difference({1,3}) # {3}

difference_update()

{1,2}.intersection({2,3}) # {2}

intersection_update()

isdisjoint()

{1,2}.issubset({1,2,3}) # True

{'a','b'}.issuperset({'a'}) # True

symmetric_difference()

symmetric_difference_update()

{1,2}.union({3,4}) # {1,2,3,4}

# https://docs.python.org/3/library/stdtypes.html#set-types-set-frozenset

# set comprehension

squares = {x**2 for x in [0,2,4] if x < 4} # {0, 4}

# unhashable type

d = {'a':1}

s = {d} # TypeError: unhashable type: 'dict'

s.add(d) # ...

# sets cannot be sorted

sorted({3,2,1}) # [1,2,3] (cuz auto casted to list)

sorted({'c','b','a'}) # ['a','b','c'] ...