Merge two lists in Python

When you merge two lists with Python, you can use the overloaded '+' operator.

a = [1,2,3]
b = [2,3,4]

>>> a + b
[1, 2, 3, 2, 3, 4]

However, when you don't want the duplicate values, you need to use set. '+' operator is not supported in a set, so use union() method.

>>> set(a).union(b)
set([1, 2, 3, 4])

You can convert a set to list with list() method.

>>> list(set(a).union(b))
[1, 2, 3, 4]

Refer to set in python document.