Python - Set literals in Python 3.X and 2.7
Introduction
In Python 3.X and 2.7, the following are equivalent:
set([1, 2, 3, 4]) # Built-in call (all) {1, 2, 3, 4} # Newer set literals (2.7, 3.X)
Sets are like valueless dictionaries, the items in set behave much like a dictionary's keys.
Here's what sets look like in 3.X; it's the same in 2.7, except that set results display with 2.X's set([...]) notation.
C:\code> c:\python33\python >>> set([1, 2, 3, 4]) # Built-in: same as in 2.6 {1, 2, 3, 4} >>> set('test') # Add all items in an iterable {'t', 'e', 's', 't'} >>> {1, 2, 3, 4} # Set literals: new in 3.X (and 2.7) {1, 2, 3, 4} >>> S = {'t', 'e', 's', 't'} >>> S {'t', 'e', 's', 't'} >>> S.add('test') # Methods work as before >>> S {'t', 'e', 's', 'test', 't'}
Demo
S1 = {1, 2, 3, 4}
print( S1 & {1, 3} ) # Intersection
print( {1, 5, 3, 6} | S1 ) # Union
print( S1 - {1, 3, 4} ) # Difference
print( S1 > {1, 3} ) # Super set
# from w w w . j av a 2s .c o m
Result
{} is still a dictionary in all Pythons.
Empty sets must be created with the set built-in, and print the same way:
Demo
S1 = {1, 2, 3, 4}
print( S1 - {1, 2, 3, 4} ) # Empty sets print differently
print( type({}) ) # Because {} is an empty dictionary
# from www. j a v a 2s . co m
S = set() # Initialize an empty set
S.add(1.23)
print( S )
Result
More set operation
Demo
print( {1, 2, 3}.union([3, 4]) ) print( {1, 2, 3}.union({3, 4}) ) print( {1, 2, 3}.union(set([3, 4])) ) print( {1, 2, 3}.intersection((1, 3, 5)) ) print( {1, 2, 3}.issubset(range(-5, 5)) )
Result
