Python add two sets and delete duplicate elements

Question

How to add two sets and delete duplicates

>>> a = set(['a', 'b', 'c'])
>>> b = set(['c', 'd', 'e'])
>>> c = a + b
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for +: 'set' and 'set'
>>>

Expected output:
c = set(['a','b','c', 'd', 'e']) 

Answer 1

Try this:

>>> a = set(['a', 'b', 'c'])
>>> b = set(['c', 'd', 'e'])
>>> c = a.union(b)

Result:

set(['a','b','c', 'd', 'e'])

Answer 2

Use union method

You want to use the union method of a set:

c = a.union(b)

https://docs.python.org/2/library/stdtypes.html#frozenset.union https://docs.python.org/3/library/stdtypes.html?highlight=sets#frozenset.union

The union method is the same as the | operator, so the line of code above is equivalent to

c = a | b

Use in-place operator

If you have no need to retain a or b, it would be better to use the update method, which will add the new members in place. That is,

a.update(b)

will produce the union in the existing data structure a. This is also performed by the equivalent code

a |= b

Sidenote: use set literal

In the code you provide, it would be faster to use the set literal notation with {element, element, ...}:

a = {'a', 'b', 'c'}

because it will execute twice as fast and not generate the unused list object.

Answer 3

You can get the union of both sets using the logical or operator |

a = set(['a', 'b', 'c'])
b = set(['c', 'd', 'e'])
c = a | b

print(c)

{'e', 'a', 'b', 'd', 'c'}

If you want the set ordered and as a list

c = sorted(list(c))
print(c)

['a', 'b', 'c', 'd', 'e']