.remove() removes element and returns None, raises KeyError if not exsit
.discard() is similar to .remove() but does not raise KeyError if not exsit
a = set(1,2,3)
for x in a:
print x
a.discard(x)This will raise RuntimeError: Set changed size during iteration
set can be initiated by list
set is unsorted.
for Python 2.7
a = {1,2,3}
print type(a) # <type 'set'>
a = {1}
print type(a) # <type 'set'>
a = {}
print type(a) # <type 'dict'>