Finding a union of lists of lists in Python

Question

Suppose we have

 temp1 = [1, 2, 3]
 temp2 = [1, 2, 3]
 temp3 = [3, 4, 5]

How do I get the union of the three temporary variables?

Expec

Answer 1

You can use the built-in set to get unique values, but in order to reach this with list objects you need first to transform them in hashable (immutable) objects. An option is tuple:

>>> temp1 = [1,2,3]
>>> temp2 = [1,2,3]
>>> temp3 = [3,4,5]
>>> my_lists = [temp1, temp2, temp3]

>>> unique_values = set(map(tuple, my_lists))
>>> unique_values  # a set of tuples
{(1, 2, 3), (4, 5, 6)}

>>> unique_lists = list(map(list, unique_values))
>>> unique_lists  # a list of lists again
[[4, 5, 6], [1, 2, 3]]